Norwegian Sponge cake (Génoise)

• Make sure you start with room-temperature eggs. The egg protein (mainly in the egg whites) will stretch and take on more air and give you more volume if they are slightly warm when you are whipping them. 
   
• Place 6 large eggs ( in their shells) in a bowl of tepid, not hot, water for 5 minutes while you gather the other ingredients.
   
• Thirty minutes or longer before baking, set an oven rack in the lower third of the oven. Preheat the oven to →350°F /175°C.
   
• Line the bottom of one 25 cm (9-inch) springform and line your springform with parchment paper. Don't grease the sides of the pan. The cakes need to cling to the ungreased pans to rise properly. 
   
• Bakers note; there is no baking powder in the recipe, as the whipped eggs will make the cake rise. 
   
• In a medium bowl, sift together the → 180-gram all-purpose flour or pastry flour and 60-gram potato starch twice. Set aside for now.
   
• Put the six large eggs, 250-gram sugar, and one to two teaspoons of vanilla bean paste in the bowl of a stand mixer and whip on low speed for one minute, then whip the egg mixture on medium speed ( speed 6 on a KitchenAid) for 10 minutes or until it triples in volume. Use a timer!
   
• After 10 minutes, turn down the speed to low- speed and slowly add 1,5 tablespoons of lukewarm water. Then continue to mix it for 5 minutes more on medium-low speed. ( speed 4 on a KitchenAid)
   
• When done, the mixture will be pale in color and slightly thickened. To test, stop the mixer and remove the whisk. Draw a figure eight with the batter dripping from the whisk. The batter should hold its shape just long enough for you to draw the "8." Remove the mixer bowl from the mixer and scrape the egg foam of the whisk attachment into the bowl. Don't tap the whisk on the side of the bowl and lose that precious air that you just used 15 minutes to create.
   
• Bakers note; Don’t fold the dry ingredients within the mixer bowl. Always transfer the egg foam to a larger, wider bowl so you can comfortably fold in the dry ingredients.
   
• Sift one-third of the dry ingredients over the egg foam, then fold in gently using a balloon whisk or a silicone spatula using gentle but decisive folding strokes until the batter is well mixed but still fluffy.  Repeat twice and make sure the flour is well incorporated each time.
   
• Often a few tiny lumps of unincorporated flour drop to the bottom of the bowl. The best way to dissolve them is to use a silicone spatula to reach the bottom of the bowl and press them out if needed.
   
• Pour into the prepared springform and bake the cake for 30 minutes; after 30 minutes, you can open the oven door to check ( and not before) or until the tops of the cake spring back when gently touched with your fingertip and a toothpick inserted into the center of the cake comes out clean.
   
• Bakers tip; touch with a finger to test if the sponge is done; if your finger makes a lasting dent, the sponge is not completely done. If the dent bounces back, take the cake out of the oven and remove the sponge cake from the oven.
   
• Immediately without delay, place parchment paper on top of the warm cake that is still in the springform, flip the springform ( with the parchment), and place it onto the wire rack. Cool until no trace of warmth remains for about 1 to 2 hours. 
   
• Once cool, gently cut around the side of the cake, remove the springform take the cake out remove the parchment paper.
   
• You can bake the cake for up to a month. After the cake is completely cooled to room temperature, wrap the cake with two layers of plastic wrap, followed by tin foil. If the cake can fit, you can also place each cake layer in its zip-lock bag. Before using your cake, remove the cake from the freezer an hour or two before you plan to fill your cake.
   
• Recommended fillings for this kind of cake are fresh fruits, lemon curd, vanilla custard, homemade jam, mousse, whipped ganache, and cream-based and mascarpone frostings and not buttercreams frostings.