Method

1. Preheat the oven to 180°C (160°C fan-forced). Line a large oven tray with non-stick baking paper.
2. To make the Chocolate Chip Cookie Dough, use an electric mixer to beat the butter, sugar and vanilla until pale and creamy. Add the egg and beat well. Sift together the flour and baking powder, add to the butter mixture with the chopped chocolate and mix on the lowest possible speed until just evenly combined. Cover and place in the fridge while making the salted peanut brownie dough.
3. To make the Salted Peanut Brownie Dough, put the dark chocolate and butter in a medium heatproof bowl over a saucepan of simmering water (make sure the base of the bowl doesn’t touch the water). Use a metal spoon to stir occasionally over low heat until just melted and smooth. Transfer to a large bowl and cool slightly. Use a balloon whisk to stir the sugar, egg and vanilla into the chocolate mixture until well combined. Sift together the flour and bicarbonate of soda, add to the chocolate mixture with the peanuts and use a wooden spoon to stir until evenly combined. Cover and place in the fridge to chill for 10 minutes or until the same consistency as the chocolate chip cookie dough.
4. Take half a tablespoonful of both doughs and roll them together into a ball, keeping the different colours separate. Place on the lined tray, with the join between the two doughs running down the centre. Flatten to about 4cm in diameter and 1cm thick. Repeat to fill the tray, leaving about 5cm between the cookies.
5. Bake in for 12 minutes or until the chocolate chip half is golden and cooked through and the brownie halves are still slightly soft to touch. Cool on the tray. Repeat with the remaining cookie doughs in two more batches.