Grease and lightly flour three 20 cm (8″) square or round sandwich tins.
Beat together the egg yolks and sugar until creamy. Then beat the butter until creamy.
Beat the egg whites until the mixture thickens. Mix the beaten butter and egg yolks together, Gradually add the flour and egg white into the mixture then add in the vanilla essence.
Divide the batter into three equal parts and sieve the cocoa into one part of batter, mix well and pour into a 20 cm (8″) sandwich tin. Pour the remaining two parts of batter into the two other tins of the same size.
Place in the oven and bake for about 15-20 minutes, starting with the cocoa batter then bake the two other tins.
