Heat the oven to 180 degrees.
Cream the softened butter and sugar together in a large bowl until nice and smooth. Attempt to keep small fingers out of bowl.
Add the eggs one at a time, mixing well each time. If cooking with kids, check for shell.
Fold in the sifted flour and the baking powder and stir through the vanilla extract. Add 2 tablespoons of milk.
Spoon 2/3rds of this mix into a large, deep cake tin.
Add the cocoa powder and the other 2 tablespoons of milk to the remaining mixture. Plop this in lumps on top of the other mix, and use a spatula to press it down into the mixture and mix it in with quick swirls – less is more here! No stirring!
Put in the oven for around an hour, until a poked in skewer comes out clean. Let it cool for 10 minutes in the tin, then turf it onto a rack. Then let it cool some more – and slice and hope!