Weigh 3 eggs in their shell, break into bowl. Add the same weight of self raising flour, of castor sugar and of softened butter. Add 1 tsp of baking powder, 25 g of cocoa and 25g of chocolate Ovaltine or similar, 1 tbs milk and beat it all up until soft and creamy.
Divide between two greased and lined 7" sandwich tins and bake at 180C for 20 -25 minutes. Leave in the tins for 5 minutes before putting onto a wire rack to cool. Meanwhile make butter cream using 100g butter, 200g icing sugar and 25g Ovaltine mixed to a paste with 2tbs milk. When the cakes are cooled beat 1 tbs boiling water into icing and use to sandwich and top the cakes.
Decorate with crushed Maltesers, or keep them whole if you prefer.