Crack the eggs and put the yolks in one bowl and the whites in another. Let both sit out for about an hour so they can reach room temperature.
6 Large Eggs, separated
Preheat oven to 325℉ (160℃)
Sift together flour and cornstarch into a bowl. Set aside.
¾ Cup All-purpose flour, ¾ Cup Cornstarch
Split the granulated sugar in half. You’ll use one half when mixing the egg yolks and the other half when beating the egg whites.
1 ¼ Cups Granulated sugar, divided
Add ½ of the granulated sugar to the bowl with the egg yolks. Using the whisk attachment begin mixing on medium speed. Continue whisking until the egg yolks are light and thick (about 3 minutes).
Add salt to the bowl with the egg whites. Using the whip attachment, begin whipping on medium speed until the whites become foamy.
¼ teaspoon Salt
Slowly pour the remaining sugar into the egg whites bowl while the mixer is still running. Increase the speed to medium-high and whip the egg whites until they hold a medium peak.
Gently fold the beaten egg yolks into the egg whites mixture.
Add ½ of the flour/cornstarch mixture to the bowl with the eggs. Fold gently until all the dry ingredients are incorporated.
Add the remaining flour/cornstarch mixture to the bowl. Fold gently until all the dry ingredients are incorporated.
Pour the sponge cake batter into an ungreased 9" x 13" baking pan. Smooth the top with an offset spatula.
Bake for 25 minutes (do not overbake). The cake will have risen and the top will be a golden color. A toothpick inserted in the center of the cake will come out clean. Remove from the oven and allow to cool for 15 minutes.
Use the end of a wooden spoon to poke holes all over the top of the cake.