Preparation
1 Preheat the oven to 180˚C/160˚C fan/gas mark 4. Line a 23cm square baking tin with tin foil and spray with cooking spray.
2 Place the chocolate and butter in a large, microwave-safe bowl. Place in the microwave and heat on high power for around two minutes until the chocolate has melted completely, stirring every 30 seconds.
3 Add the sugar, eggs, vanilla and cocoa and stir well to combine. Add the flour and stir again. Pour the batter into the prepared tin.
4 In a bowl, stir together the peanut butter, melted butter and icing sugar. Drop spoonfuls of the swirl mixture over the top of the brownie mixture, then use the tip of a butter knife to swirl the two together.
5 Bake for 25-30 minutes until a toothpick inserted into the centre comes out clean. Allow to cool, then slice into individual brownies.