1. To prepare cake base, beat together margarine and confectioners’ sugar. Add egg whites. Lower mixer speed and add flour and cocoa. You should have a thick, brown batter. Arrange silicone baking mat on a cookie sheet lined with Gefen Parchment Paper. Using a flat spatula, spread the batter over the baking mat. Make sure the batter fills all the crevices of the design. Freeze batter for 10 minutes.
2. Preheat the oven to 300 degrees Fahrenheit (150 degrees Celsius). To prepare the white cake, beat 3/4 cup sugar, flour, whole eggs, and melted margarine. Transfer to a separate bowl and rinse beater very well. Beat together egg whites with two tablespoons sugar until firm. Using a rubber spatula, fold the first mixture into the egg white mixture until you have a uniform batter.
3. Remove the silicone mat from the freezer and pour the white cake batter onto it. Smooth with a spatula. Bake for just six minutes. (As there are differences in oven temperatures, you might need another two to three minutes.) Check that the cake is done with a clean finger; when the cake does not stick, it is ready.
4. Allow the cake to cool, and turn it onto a sheet of parchment paper. Gently lift off the silicone mat. Now you have a white cake with a brown decorative design.
5. Line the depressions in your mold with a sheet of plastic wrap. Cut the cake down the middle, and divide each half into three strips that are 6 and 1/2 inches (17 cm) long. You should have six strips that are exactly the size of the depressions in the mold. Line each depression with a strip of cake.