Preheat the oven to 180'C. Line an 8-inch / 20cm square baking tin with baking paper and set aside. Break the chocolate into a bowl and melt over a bowl of boiling water. Once melted set aside to cool slightly while you start the rest of the recipe.

Melt the butter in the microwave and add to a large mixing bowl with the sugar. Using an electric whisk, mix together until combined.

Add the eggs and vanilla extract to the sugar/butter mix. Continue to mix with electric whisker for a minute until the mixture pales and starts to go fluffy.

Add the chocolate to the mix - make sure it is warm but not too hot or it will cook the eggs (not good!). Using a spatula fold the chocolate in and mix until combined.

Sift in the flour and cocoa powder. Add the salt and then fold the dry ingredients into the mix gently. You don't want to over mix - just enough so there are no lumps of flour. Once combined, pour into the lined baking tin and spread out evenly. Smooth out the top with a spatula.

Next spoon the peanut butter over the top of the mixture evenly and then use a knife to swirl it into the brownie mixture.

Place the brownies in the oven and bake for 30 minutes.

Remove from the oven and cool on a wire rack completely before cutting them up. It is very important to ensure the brownies cool completely before cutting (at least 2-3 hours). They should be a bit wobbly still when they come out of the oven but will firm up as they cool.