Vanilla Sponge Cake
 

• Twenty minutes or longer before baking, Set your oven rack in the center of the oven, And preheat the oven to 170C°/ 338F°. Using an oven thermometer will ensure even baking results each time, as every oven is different. Always go with the reading on your oven thermometer rather than the temperature you set on your oven.
   
• Grease your wire racks lightly with butter and set them aside; this step will prevent the cake from sticking to the wire rack.
   
• Use a small piece of cold butter, and gently rub the cold butter over the bottom and the sides of two 20 cm ( 8-inches) round baking pans. This technique of using a small piece of cold butter ensures an even, ultra-thin coating. Place a circle of parchment in the bottom of the pan. Add a tablespoon of all-purpose flour and tap it around the inside of the pan until all the buttered surface is covered 100%, then turn the pan upside down over a sink and tap out the excess flour. If you don’t have two pans, it’s okay to bake the cakes in stages; The cake batter will be kept at room temperature until needed.
   
• Bakers Note: All-purpose flour with 8-9% gluten is ideal for tender sponge cake layers; I use 9%. Although 10% works, less gluten is preferable. You can enhance tenderness by mixing in potato starch. Potato starch is my secret ingredient in this vanilla sponge cake. It's very pure and feels silky between the fingers. Do not substitute potato starch for cornstarch. They may look the same and behave similarly, but potato starch is lighter than cornstarch, bakes more thoroughly in cake batter, and yields a softer sponge cake.
   
• Combine 110-gram all-purpose flour or pastry flour, 50-gram potato starch, and 1 teaspoon baking powder in a medium bowl. To get the cake layers you truly deserve, sift the flour mixture a few times to get the flour as aerated and light as possible.
   
• Bakers note: The egg white to yolk ratio in an egg can vary to such a degree. Therefore, weighing the egg yolks and egg whites as mentioned in the recipe and adding or reducing them if needed is advisable.
   
• Wipe your mixer bowl with a paper towel dampened with a little lemon juice to eliminate any trace of grease so that the meringue whips up well. In a clean bowl of a stand mixer fitted with the whisk attachment, put 210 grams of egg whites and a pinch of cream of tartar; whip the meringue on medium speed until the meringue is white, glossy, and holds a soft peak before adding any sugar. This allows the meringue to keep its volume and not deflate when adding the sugar.
   
• Then add one tablespoon at a time 200 grams of superfine sugar, and continue mixing on medium-high speed for 3 minutes more to make a very shiny and thick meringue ( Use a timer!) 
   
• As soon as all of the sugar is incorporated and the meringue is thick, Stop the mixer and add 140-gram egg yolks ( all at once) and whip on medium-high speed for 7 seconds and not a second longer, or your cake will become flat and dense. Stop the mixer and remove the bowl from the mixer. 
   
• Sift half of the flour/potato starch mixture over the whipped meringue/yolk mixture and gently combine with a balloon whisk until well incorporated; repeat this step one more time. Scrape the side and the bottom of the mixer bowl with a silicone spatula to make sure all the flour is integrated. Set aside for now.
   
• In a small saucepan, warm 50-gram heavy cream and one teaspoon vanilla bean paste over medium heat until warm ( about 60 seconds, 50C°/122F° ), then quickly pour the warm cream around the edge of the bowl, add lemon zest if using and gently combine with a spatula without deflating the batter too much.
   
• Divide the sponge cake batter between the two prepared pans. About 360 grams in each pan. Use a scale! Give the cake pans a little spin to settle the cake batter.
   
• Bake both cakes until golden brown and the top of the cake feels firm and springs back when pressed lightly in the center, about 18 to 20 minutes, depending on your oven and baking pan. Mine was done at 19 minutes. To check if a vanilla sponge cake is ready after 18 minutes of baking, you should first look through the oven window rather than open the oven door. If the center appears slightly sunken, give it a minute or two longer while keeping an eye on it. At the 20-minute mark, if the center seems almost set, carefully open the oven and gently press the top of the cake. It should feel firm to the touch and may have a slight bounce to it. This method allows you to monitor the cake's progress without disrupting the baking process.
   
• Remove the cake from the oven, immediately without any delay, run a knife between the sides of the pan and the cake, and invert the cakes immediately onto a wire rack; remove the parchment paper and leave it to cool completely on a wire rack. 
   
• Cover the cake layers with plastic wrap or in a large ziplock bag to prevent them from drying out until you are ready to use them.
   
• Cut both cake layers horizontally to create four even layers., I use a cake leveler; I move the leveler back and forth like a saw; you´ll glide the leveler feet on your work surface to cut your cake. Keep them covered in plastic wrap until you are ready to assemble your cake.

lemon curd
 

• If you are going to add lemon zest to the lemon curd, be sure to scrub the lemons with a little liquid dishwashing detergent, rinse well, and dry before zesting. I use a Microplane zester to collect all the wonderful lemon zest.
   
• Before juicing the lemons, give them a good roll on the work surface to release as much juice as possible.
   
• In a large bowl add 90 grams powdered sugar, 17-gram cornstarch, 2 large eggs, one egg yolk, zest from 1 lemon ( optional), 125 grams freshly squeezed lemon juice, whisk it all together into a homogenous mixture using a whisk or an immersion blender.
   
• Pour the content of the bowl into a medium-size saucepan and cook over medium-low heat, constantly stirring with a whisk or spatula and scraping the sides of the pan as needed, until thickened to a consistency resembling pudding. This step takes about 5 minutes.
   
• When the lemon curd has thickened slightly, like pudding, remove from heat, add in 75-gram cold heavy cream, and stir to combine.
   
• Transfer the lemon curd right away to an airtight jar or a bowl. Press a piece of plastic wrap against the lemon curd to create an airtight seal and chill in the fridge until needed.
   
• The Lemon curd will keep refrigerated in an airtight container for two weeks. (Longer storage dulls the fresh citrus flavor.)

Whipped Greek Yogurt Frosting 
 

• Baker's Note: Greek Yogurt with 10% fat should not be watery; it should be thick. If the Greek yogurt you bought seems watery, do the following: Place a fine-mesh strainer over a small bowl and place the Greek yogurt in the strainer. Wrap with plastic wrap and place in the fridge to drain for a few hours, preferably overnight. This step is crucial. Otherwise, the Whipped Yogurt Frosting will be too watery and will not form a properly whipped Greek Yogurt frosting. Depending on how much liquid your Greek yogurt initially contains, you might lose half its volume in straining, so plan accordingly.
   
• For best results, place the heavy cream and Greek yogurt out of the fridge and chill both in the freezer for 15 minutes before you start. If you don't have a freezer, make sure your cream and Greek yogurt are really cold. Slightly warm cream does not whip well.
   
• In the bowl of your stand mixer fitted with the whisk attachment, add 75 grams of sifted powdered sugar, 350 grams of cold Greek yogurt (10% fat), 350 grams of cold heavy whipping cream (40% fat), and one teaspoon of vanilla bean paste. If using a fresh vanilla bean, use a sharp knife to split the vanilla bean lengthwise and scrape the seeds into the mixing bowl.
   
• Whip the mixture at low speed for one minute, then turn the mixer to medium-high speed until the yogurt frosting is thick, fluffy, and stable, about 1 to 3 minutes. Whipped yogurt frosting destabilizes (softens) when overmixed, so keep an eye on the frosting as soon as it thickens.
   
• For this recipe, you'll need two-thirds of the whipped Greek Yogurt Frosting for the blueberry filling, and the other third for the coconut filling. Not a fan of coconut? just leave out the desiccated coconut.

Greek Yogurt Blueberry filling
 

• In a medium saucepan, add 250 grams of frozen blueberries, 2 teaspoons of white sugar, and freshly squeezed juice from 1 lemon. Warm over medium heat just to soften the blueberries, stirring occasionally, but you want the blueberries to remain intact. This should take about 3-5 minutes.
   
• Remove from heat. Strain the soft blueberries through a fine-mesh sieve, Place the soft blueberries still in the fine-mesh sieve in the fridge to get cold, and too drain as much blueberry juice as possible, without pressing on the blueberries. About 20 minutes.
   
• The leftover blueberry juice is delicious when combined with sparkling water, try it you´ll love it.
• Pull the cold soft blueberries out of the fridge, and make sure that the blueberries are well drained or your cake layers will become too soggy.  
   
• Remove two-thirds of the Whipped Greek Yogurt ( about 500 grams ) add all of the soft blueberries to the 500 gram Whipped Greek Yogurt Frosting and combine with a spatula.
   
• If not using immediately, place in the fridge until you are ready to fill your cake layers.
   

Greek Yogurt Coconut filling
 

• Combine 15 grams of desiccated coconut (optional) with the remaining 250 grams of Whipped Greek Yogurt, and place in the fridge until you are ready to assemble the cake layers

Assembling
 

• Place the first cake layer, cut side up, on a cake stand. Add half of the Greek Yogurt blueberry filling on top of the first cake layer, and smooth it all the way to the edge using an offset spatula. Add the second cake layer on top, and press down lightly to help it adhere to the filling; this action ensures the layers hold together when cut.
   
• Add the Greek yogurt Coconut filling on top of the second cake layer, smoothing it out to the edges with an offset spatula. Add a few spoons of lemon curd on top. Add the third cake layer on top, and press down lightly to help it stick to the filling.
   
• Add the remaining blueberry filling on top of the third cake layer, and smooth it out to the edges using an offset spatula. Place the final (fourth) cake layer on top, pressing down lightly to help it adhere to the filling. Cover the entire cake with plastic wrap to seal it completely. If you have an adjustable cake ring, place it around the cake. 
   
• Chill in the refrigerator for at least 4 hours.

Angel Feather Icing
 

• Wipe the inside of your bowl and the whisk attachment with a paper towel dampened with a bit of lemon juice to eliminate any trace of grease. Ensure the bowl and beaters are thoroughly clean; even the slightest hint of oil can inhibit the foaming.
   
• For best results, use fresh egg whites. Often, boxed whites don’t whip up as well. Ensure you cleanly separate the egg whites from the yolks.
   
• Fill a saucepan with 3 cm (1 1/2 inches) of water and place it over medium-low heat.
   
• In the bowl of a stand mixer, combine 100 grams of egg whites, 255 grams of white sugar or superfine sugar, 50 grams of water, 60 grams of glucose (or light corn syrup), a pinch of cream of tartar, and seeds from 1/2 vanilla bean (if using). Use a clean whisk to make a slurry.
   
• Place the bowl over the steamy water, stirring and constantly scraping with a whisk or spatula until all of the sugar is 100% dissolved. With gently simmering water, the meringue should cook fairly quickly; this step typically takes about 3 minutes. If you find the temperature climbing too slowly, you can increase the heat slightly.
   
• To check if the sugar is dissolved, rub some of the egg white/sugar mixture between your (grease-free) thumb and forefinger. If it doesn't feel grainy, your sugar is dissolved.
   
• Transfer the bowl to a stand mixer fitted with the whisk attachment. Whip on medium-high speed until the mixture is glossy, thick, and has tripled in volume, or until you are satisfied with the consistency of the Angel Feather Icing. This usually takes about 5 minutes.

With a hand mixer

• Baker's Note: Egg whites begin to coagulate at approximately 65°C/149°F, so make sure that the water is just at a simmer when you place the deep bowl into the saucepan. Start beating immediately at the lowest speed with an electric hand mixer as soon as you place the bowl into the simmering water, or you risk making scrambled egg whites!
   
• Put the 100-gram egg whites, 255 grams of sugar, 50 grams of water, 60 grams of glucose (or light corn syrup), a pinch of cream of tartar, and seeds from 1/2 vanilla bean into a spotlessly clean bowl. Use a small whisk or spatula to make a slurry.
   
• Baker's Note: Heating the egg whites over a pot of simmering water relaxes their proteins, enabling them to whip up higher and more quickly. The sugar also dissolves, resulting in a silky-smooth consistency.
   
• As soon as your water is at a simmer, turn off the heat and immediately place your bowl in the simmering water, ensuring it goes up 2 1/2 cm (1 inch) up the side of the bowl. Start beating immediately at the lowest speed with an electric beater until the sugar is 100% dissolved. (This takes about 3 minutes).
   
• "As soon as the sugar is 100% dissolved, continue to whip on medium-high speed (with the bowl still in simmering water) until the mixture climbs to the top of the bowl and the meringue holds a soft, floppy peak, about 4 minutes."
   
• Remove the bowl from the heat and continue beating at medium-high speed until the frosting is cool and you are satisfied with the consistency of the Angel Feather Icing. This takes about 3 to 5 minutes.
   
• For maximum freshness and deliciousness, use it immediately to decorate your cake.

• Pull the cake out of the fridge, and remove the cake ring and plastic wrap. 
   
• Pile a generous amount of angel feather icing on top of the cake. Using a metal spatula, evenly spread the frosting, working your way from the top down towards the sides, ensuring a smooth and even coat. For a decorative touch, utilize the back of a spoon to create elegant swirls in the frosting, adding a whimsical texture to the icing.
   
• While the cake maintains its moistness for several days, it is best enjoyed within 24 hours, due to the Angel Feather Icing.
   
• Keep leftovers covered in the fridge.