Measure flour, baking powder, salt, sugar and cornstarch into 8-inch square (glass only) baking pan. Pour milk into dry ingredients. Add slightly beaten egg yolks from separated eggs, melted butter and vanilla extract. Wire whip to blend. Will be a soupy batter. Bake for 50 minutes until cake pulls away from pan sides.
Chocolate Frosting 1/2 cup confectioners' sugar 2 tablespoons baking cocoa 3 tablespoons hot water
While still warm pour a drizzle of this mixture over cake from measuring cup. Serve warm.