Line a 20 × 20 cm tin with baking parchment.
Mix 120 g peanut butter with the maple syrup and melted coconut oil until smooth.
Add the oats and stir until completely coated. The mixture should hold together when pressed.
Transfer to the tin and compact it very firmly into an even layer.
Refrigerate for 30 minutes.
Gently melt the dark chocolate with 48 g peanut butter, stirring until smooth.
Pour the topping over the chilled base and spread evenly.
Sprinkle with chopped peanuts and refrigerate for 30–60 minutes, until firm.
Lift the slab out of the tin and cut it into 12 bars with a warm, dry knife.