Preheat oven to 180ºC. Grease an eight inch round tin. Sieve self-raising flour with baking powder, salt and cocoa powder.
Mix together softened butter with sugar and beat well with a wire whisk or electric beater till light and fluffy. Mix in one egg at a time.
Fold in flour and cocoa mixture two to three spoons at a time, taking a little of buttermilk to make a smooth batter. Lastly mix in vanilla essence.
Pour batter in prepared cake tin and bake at 180ºC for thirty five to forty minutes.