Step 1

Whip eggs and sugar: Whip 4 eggs in a stand mixer on high speed until foamy (~2 min) then gradually add 1 cup of granulated sugar 1 tablespoon at a time, while continuing to whip. Then, whip until the mixture falls off the whisk in a thick ribbon that doesn't disappear for 1-2 seconds (~20 min; or more if using a hand mixer).

Step 2

Prep: Meanwhile, preheat the oven to 350F with the rack centered. Line an 8-inch round cake pan (at least 2" tall) lined with foil or parchment and spray with nonstick spray. Alternatively, you can brush room temperature butter on the inside of the pan, then dust it with flour, knocking out the excess to make the surface non-stick.

Step 3

Optional: Fasten the wet baking strips around the baking pan for an evenly risen cake (optional). The baking strips ensure that the cake rises evenly and doesn't form a dome.

Step 4

Sift dry ingredients: Sift 1 cup all-purpose flour and 1 tsp baking powder, twice.

Step 5

Mix liquids: In a cup whisk together 2 TBSP melted butter, 1 TBSP hot water and 1 tsp of vanilla extract.

Step 6

Fold in dry ingredients: add the dry ingredients into the whipped eggs in halves, carefully folding with a spatula forming the number 8 with each stroke. Do not overfold or the cake will be dense and doughy. Just fold enough to barely incorporate the flour.

Step 7

Next, Fold in the liquids and carefully keep folding the batter until thoroughly incorporated. Do not overmix or the cake will be dense.

Step 8

Bake: Pour the sponge cake batter into the prepared baking pan. Bake for about 35 minutes or until a toothpick inserted into the center comes out clean. Do not open the oven to check until you can smell cake in the kitchen (~30 min).

Step 9

Remove the sponge cake to a cooling rack and allow to sit undisturbed for 5 minutes. Then invert it onto a cooling rack and remove the foil or parchment. Allow to completely cool before using.

Step 10

Let rest: For best results wrap the cooled cake in plastic and leave on the counter for 6-8 hours before using in a cake. This will reduce the amount of crumbling when you split the cake layer in two horizontally.

Step 11

How to split the cake in two horizontally: place the palm of your non-dominant hand over the top of the cake and keep rotating it as you, use your dominant hand to hold a long serrated knife, and start scoring the outside of the cake, about 1/2 inch deep, going all around the cake. Continue going in circles scoring deeper and deeper until you get to the center. The easiest method: attach these two cake leveler pieces on two opposing ends of the knife blade, then just cut the cake horizontally by moving the knife back and forth in a back and forth motion while keeping the knife perpendicular to the surface. The levelers will ensure that the knife stays level all throughout the cutting.