Preheat oven to 180 degrees. Grease and line a loaf pan.
Melt the butter and chocolate for the brownie layer. Allow to cool slightly.
Whisk in the eggs and sugar till melted and well combined.
Fold in the rest of the ingredients and pour into the prepared tin. Bake for 10 minutes.
Meanwhile, beat butter and sugar till fluffy. Add one egg at a time and beat till incorporated.
Sift in the flour, baking powder and salt into the beaten mixture.
Add the milk and vanilla, and beat till just combined. Do not overbeat.
Take out the brownie and spread the butter cake mixture on top.
Bake for 25 to 40 minutes, till a skewer inserted in the center comes out clean.
Cool in pan for five minutes and then cool completely on a rack. Slice and enjoy!