Pistachio Sponge Cake

• Using finely grated pistachio will create a more moist texture in the sponge cake. When you finely grate the pistachios, they can distribute more evenly throughout the cake batter, helping to retain moisture and add a subtle nutty flavor. Finely grated pistachios will make your sponge cake a bit more moist compared to using chopped or coarsely ground pistachios.
   
• Baker Note: "When preheating the oven for my cakes, always use the 'top and bottom heat' setting. Please avoid using the fan-forced option, unless otherwise specified." Twenty minutes or longer before baking, set your oven rack in the center of the oven, and preheat the oven to 170°C (338°F).
   
• Grease your wire racks lightly with butter and set them aside; this 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-inch) 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 100 grams of all-purpose flour and 50 grams of potato starch (or an additional 50 grams of all-purpose flour instead of potato starch) with 1 teaspoon of baking powder in a medium bowl. Sift the mixture a few times to get the flour as aerated and light as possible.
   
• Bakers Note: When I grate my pistachios, I use the grinder attachment on my ankarsrum mixer to finely grate 150 grams of raw pistachios. If you're using a food processor, take about 50 grams of the sifted flour mixture and process it with the 150 grams of raw pistachios until you have a very fine powder. 
   
• Baker Note: An egg's white-to-yolk ratio can vary. It’s therefore advisable to weigh the egg yolks and egg whites and add or reduce them if needed.
   
• Baker Note: 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 it is climbing to the top of the bowl and the meringue is white, glossy, and holds a soft, floppy peak. About 3 minutes. Use a timer!
   
• As soon as the meringue is glossy, add one tablespoon at a time of 200 grams of superfine sugar, and mix 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, with your mixer on medium speed, add the 140 grams of egg yolks (all at once) and whip for 7 seconds and no longer, or your cake will become flat and dense. Stop the mixer and remove the bowl from the mixer.
   
• Baker Note: Instead of using a large spatula for maximum volume, use a balloon whisk to fold the flour mixture into the cake batter. A spatula will deflate the cake batter more.
   
• Sift one-third of the flour mixture over the whipped meringue/yolk mixture and gently combine with a balloon whisk until well incorporated; repeat this step twice. Use a large silicone spatula at the end of the folding to scrape the side and the bottom of the mixer bowl to make sure all the flour is integrated. Set aside for now while you warm the cream.
   
• In a small saucepan, warm 75 grams of heavy cream and 1 teaspoon of vanilla bean paste over medium heat until warm (about 60 seconds, about 50°C/122°F), then quickly pour the warm cream around the edge of the bowl and gently combine with a balloon whisk or spatula without deflating the batter too much.
   
• Carefully fold in the 150 grams of grated pistachio  in the cake batter in two additions until evenly incorporated. Make sure to check the bottom of the bowl as well; if the grated pistachio is not thoroughly incorporated in the cake batter, the cake will bake unevenly.
   
• Use a scale to weigh the cake batter, then divide the cake batter between the two prepared pans—about 450 grams in each pan. Give your pans just a really good spin on the table; what that does is it takes the cake batter up the side of the pan a little bit, just so that as it's baking, it already has an attachment to kind of move up the side of the pan. So, don't be afraid to really give it a good spin. Get that batter moving up. Don’t tap your baking pans on the kitchen counter to try to get things to level out, especially with this style of cake batter, because banging your pans or dropping them on the table to level the batter actually gets rid of all the air bubbles that you just incorporated into the batter.
   
• Baker Note: 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.
   
• Bake both cakes until golden brown, firm on top, and the cake springs back when pressed lightly in the center, about 19 to 22 minutes, depending on your oven and baking pan. Mine was done at 20 minutes. To check if the 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.
   
• Then immediately, without 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 place them in a large ziplock bag to prevent them from drying out until you are ready to use them.
   
• Once you’ve baked the two layers, you have a choice: You can use them as they are, or you can split each one in half to make a four-layer cake. It’s all about how much frosting/filling you have made for your cake. Keep in mind four layers mean more frosting/filling. It also means more height.
   
• To 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.
   
• It is easier to cut into layers when it is semi-cold; wrap each individual cake with 2 layers of plastic wrap, followed by tin foil, or place it in a ziplock bag. Freeze for 1-2 hours before you cut the cake into 4 horizontal layers. Having chilled cake layers is much easier to cut.
   
• You can bake the pistachio sponge cake layers up to a month in advance and freeze the cake. After the cake is completely cooled to room temperature, wrap each individual cake with 2 layers of plastic wrap, followed by tin foil, or place it in a ziplock bag. Before using your cake layers, remove the layers from the freezer about an hour before you plan to fill the cake.
   
• This cake is a great match with any cream-filled fillings.