Chocolate Buttermilk Cake

cake:
185g of butter
1 teaspoon of vanilla essence
1½ cups of castor sugar
4 eggs, separated
¾ cup of self-raising flour
one third cup of cocoa
¾ cup of of buttermilk

filling:
200g of dark chocolate (melted)
90g of butter (melted)

Grease two round cake tins and line with baking paper.
Cream butter, sugar and vanilla essence in a small bowl
until light and fluffy, then beat in egg yolks until just combined.

Transfer mixture to a large bowl ; stir in sifted flour and cocoa
and buttermilk.

Beat egg whites until stiff and fold lightly through
cake in two batches. Pour mixture into tins.
Bake at 180º for 45 minutes or until skewer comes away clean.

Combine melted chocolate and melted butter, stir until smooth.
Stand until spreadable. Use as filling and icing for the cake.