Start by pre-heating your oven to gas mark 4.
Line a rectangular cake tin with grease proof paper.
Melt the butter in a pan along with the chocolate and sugar.
Once melted completely, allow to cool slightly.
Next whisk in the eggs, one at a time.
Fold through the flour and cocoa until combined.
Pour half of the brownie batter into the tin.
Spoon roughly 7 or 8 tablespoons of peanut butter over the batter and do your best to spread out in an even layer.
Pour the remaining half of the batter on top of the peanut being careful not to disturb it too much.
Dollop a few more tablespoons of peanut butter on top and, using a toothpick or something simillar, swirl the peanut butter into the top layer of brownie mix.
Bake in the centre of the oven for 25-30 minutes or until a crust has formed on top of the brownies but they are bouncy to the touch.
Allow to cool slightly before slicing and serving.