The butter stir well to snow. Add sugar, vanilla, egg yolks, zest and mix until a foamy cream. The oven was heated to 175 C, and the shape of the cake smeared with oil and sprinkled with flour. Flour mixed with baking powder and add it little by little frothy cream until a cake batter. Egg whites are broken down into a thick foam. First pour 1/3 of the egg whites into the dough and then the residue, gently stir with a spoon. Half of the dough is poured into the form, and the other half is stirred well with the cream or milk and cocoa and then poured onto a light part in the mold. Pass through the middle of the dough fork, to obtain a marble pattern and baked. Once ready, sprinkle with powdered sugar.