Finely grind the biscuits with the sugar (in a blender or with a hand blender). Melt the butter and add to the biscuit flour. Add the peanut butter and mix everything well. Put everything in a brownie tin (approx. 25 x 25 cm) lined with baking paper and press evenly.
Melt the chocolate and spread it over the mass. Put everything in the refrigerator for at least 3 hours.
Remove from the mold and cut into cubes with a warm knife.