Line and grease a brownie pan and set aside. Preheat oven to 180 degrees.
Melt the butter and chocolate till homogenous. Allow to cool slightly.
Beat the eggs, sugar and vanilla till well combined and fluffy. Add the melted mixture and continue to beat till done.
Sift in the flour and cocoa powder. Fold in the mixture. Pour into the prepared pan and flatten the top.
Beat together the ingredients for the peanut butter layer. Drop spoonfuls on the brownie batter and swirl with a fork to spread.
Bake for 30 minutest till the top looks done. Cool in pan for 5 minutes. Slowly pull out from the pan and cool on rack completely. Slice and serve.