In a bowl using hand mixer,mix your butter and sugar on a high speed for like 3 to 5 minutes till it becomes fluffy

Add egg 1 by 1 and mix together on low speed

In a separate bowl sieve your flour together with the baking powder,then add the flour to the butter mixture bit by bit, divide the cake mixture in to two add cocoa powder to one and mix well

Then rub butter to your baking pan spread the cake batter randomly and bake