Food & Cooking Recipes Chocolate Sheet Cake Be the first to rate & review! By Martha Stewart Test Kitchen Martha Stewart Test Kitchen The recipes developed by our test kitchen team have undergone a rigorous process of development and testing, ensuring that every element is optimal, from ingredient amounts to method and cooking time. This process includes triple-testing recipes to ensure they meet our high standards. The many stellar cooks and food editors who have been part of our team include Sarah Carey, Lucinda Scala Quinn, Jennifer Aaronson, Shira Bocar, Anna Kovel, Greg Lofts, Riley Wofford, Lauren Tyrell, and Lindsay Leopold. Editorial Guidelines Updated on June 12, 2017 Print Rate It Share Share Tweet Pin Email Yield: 1 10-by-15-inch cake This is a moist, all-purpose sponge cake. Ingredients ½ cup all-purpose flour ½ cup unsweetened cocoa powder Pinch of salt ½ teaspoon baking powder 4 large eggs, separated 1 cup sugar 3 tablespoons boiling water 1 teaspoon vanilla Directions Heat oven to 350 degrees. Butter and flour, or line with parchment, a 10 1/4-by-15 1/4-by-3/4- inch jelly-roll pan. Sift together flour, cocoa, salt, and baking powder. Set aside. Beat together egg yolks and sugar until fluffy. Beat in boiling water and vanilla. Fold in dry ingredients in three additions. Beat egg whites until stiff but not dry and whisk a quarter of them into batter. Fold in remainder of whites and spread batter evenly in pan. Bake about 15 minutes or until cake springs back when gently pressed. Cool in pan. Rate it Print