Turn the oven on to 180 C / Gas 4. Grease two sponge tins and line with parchment.
Cream the butter and sugar together, until light and fluffy.
Then sieve the flour into the mix, along with the baking powder, and cocoa powder.
Whisk the eggs and milk together and add them to the mix, mix until light and fluffy. Split the mix between the two tins and spread out evenly.
Put in the oven for 20 to 30 minutes, or until your knife comes out clean after putting it in the middle of the cake.
When cooked, turn the cakes out on a wire wrack and leave to cool completely. Whilst your cakes are cooling, cream the butter, icing sugar and milk together in a bowl, along with the cocoa powder, the end result should be a creamy mix.
When the cakes are cooled, decide which cake will be the top and the bottom of your sponge. Turn the bottom sponge onto a plate, or a cake stand, smother the chocolate buttercream all over, making sure it gets to the edges. Then, place on the top sponge. Dust with icing sugar to finish, enjoy!