Step 1

Preheat oven to 180°C. Grease a 19cm x 29cm slice pan and line the base and sides with baking paper, allowing the 2 long sides to overhang.

Step 2

Use an electric mixer to beat the butter and combined sugar in a bowl until pale and creamy. Beat in the egg. Add the flour, cocoa powder, baking powder and milk and stir until just combined. Stir in the chocolate.

Step 3

Spoon the chocolate mixture, alternating with peanut butter, into the prepared pan. Use a round-bladed knife to gently marble. Smooth the surface. Sprinkle with biscuit pieces and dark chocolate. Bake for 30 mins or until a skewer inserted in the centre comes out clean.

Step 4

Set aside in the pan to cool completely. Cut into pieces to serve.