Preheat oven to 170°C fan (180°C conventional). Line a 8in square baking tin (deep brownie tin) with parchment paper.

Melt the chocolate in a bain marie (a medium bowl set over a pan of simmering water) and once half melted, add in the cubed butter and stir until well blended.

Remove the melted chocolate from the heat and beat in the sugar and salt using a handwhisk. Set aside to cool for five minutes before stirring in the eggs to a smooth batter.

Meanwhile, sieve the flour and baking powder together and in two batches, fold the sieved ingredients into the chocolate mixture.

Pour the mixture evenly into the prepared tin. Before baking, drop spoonfuls of peanut butter on top, then using a small spatula, lightly draw the peanut butter through the surface to create a swirl.

Bake on the middle shelf of the oven for 25-30 minutes or until slightly crispy on the top. When baked, the mixture should still appear slightly tacky when a skewer is inserted into the centre. Allow to cool in the tin, before lifting the brownies in the parchment onto a work surface. Use a large knife to cut across into 16 squares.

Variation: Add a nutty crunch to these brownies with some chopped roasted peanuts. If you want to avoid nuts, an alternative to peanut butter is to swirl salted caramel into the topping.