PREPARATION:
Step 1:
Prepare the oven’s temp at 350 degrees Fahrenheit (177 degrees Celsius). Grease a 12×17-inch baking pan with nonstick cooking spray or butter, and then line it with parchment paper to ensure that the cake releases without difficulty.
Step 2:
Using a hand mixer or stand mixer equipped with a whisk attachment, whip the egg whites and sugar in a medium bowl on high speed for 5 minutes, or until firm peaks form. Put aside.
Step 3:
In a separate bowl, mix the egg yolks, remaining sugar, and vanilla extract for approximately 2 minutes, or until light and creamy.
Step 4:
In a large basin, sift the flour, cocoa powder, baking powder, and salt together. Pour the combination of melted butter, espresso, and egg yolks over the dry ingredients. Mix all ingredients at medium speed until well blended.
Step 5:
Using a rubber spatula or wooden spoon, carefully fold the egg whites into the batter until well incorporated. Avoid over-mixing the whites and deflating them. The batter will be rather airy.