1. Preheat the oven to 350 degrees Fahrenheit (180 degrees Celsius). Spray a bundt pan or 9- x 13-inch baking pan with baking spray or oil.
2. Beat the egg whites until they are stiff. Set them aside.
3. Combine the flour, baking powder, and salt; add this to the batter alternately with the juice. Mix just until it is blended.
4. Gently fold in the beaten egg whites.
5. Pour two-thirds of the batter into the pan. To the remaining one-third of the batter, gently mix in the cocoa. Pour this over the white batter. Cut through the batter with a knife a few times to make a marbled design.
6. Bake for approximately one hour for a bundt pan or 45 minutes for a 9- x 13-inch pan. A toothpick inserted should come out clean with no batter clinging to it. Cool for 20 minutes in the pan. Remove the cake from the pan and sprinkle it with confectioners’ sugar or frost it with chocolate frosting (see below).
7. Combine the egg yolks, sugar, vanilla, oil, and applesauce, and beat until the mixture is light, about five minutes.