Sift together flour, cocoa powder, and baking powder.
Cream the butter and sugar together.
Add eggs one at a time, mixing well after each addition.
Mix in the sifted dry ingredients and milk until combined.
Pour the batter into the cake pan.
Bake in a preheated oven at 180°C (356°F) for 25–30 minutes.
Let it cool, then cut into desired sizes.