Preheat the oven to 170°C. Line a 23cm square brownie tin with baking paper.

To prepare the peanut butter swirl, place the cream cheese, vanilla, egg and sugar in a bowl and whisk until smooth. Add the peanut butter and whisk again until smooth and creamy. Set aside.

To make the brownie mix, whisk the eggs and sugar (from the kit) until light and creamy, then stir in the melted butter. Add the brownie mix and chocolate chips and stir until well combined.

Pour half the brownie batter into the prepared brownie tin and using a tablespoon, drop half the peanut butter swirl mixture in big dollops on top. Repeat with the remaining brownie mix and finish off with the remaining peanut butter swirl mix. Use a small pallet knife to swirl through and marble the two mixtures.

Place in the preheated oven and bake for 25-30 minutes until just cooked, but still gooey and fudgey inside. Remove from the oven and allow to cool completely before cutting into squares.