Preheat the oven to 180°C. Line two 20cm cake tins, a 15cm cake tin and a baking sheet with baking paper. Grease with nonstick spray.
1. Beat the butter and sugar in a bowl until pale and creamy. Add the eggs one at a time, beating each in until combined.
2. Sift the flour, baking powder and cocoa powder into a separate bowl. Add to the butter mixture. Pour in the milk and beat until just combined.