Scatter the mixture evenly into the lined pan and press down. Bake for 6 minutes.
Once baked, immediately spread the warmed peanut butter over the oreo base. Evenly scatter the chocolate chips over the peanut butter. Completely cover with the halved marshmallows (or mini marshmallows), placing them cut side down.
1/2 cup (8 tbsp) peanut butter, 1/2 cup (90g) milk / semisweet chocolate chips or chopped chocolate, 24 large marshmallows (or vegan marshmallows)
Place under a broiler (oven grill) for under 1 minute to toast the marshmallows (watch them closely!) - mine took around 30 seconds.
Remove from the oven and immediately scatter the chopped peanut butter cups over the marshmallow layer.