Preheat the oven to 190C/375F and line two baking trays with parchment paper. Make the topping. In a large mixing bowl, rub the butter into the flour and sugar with your fingertips, until a soft, crumbly dough is formed. Add the chopped and whole peanuts, then set aside.
Prepare the cookie dough by creaming cream the sugar, butter and peanut butter in a separate mixing bowl. Add the egg and beat again. Sift in the flour, cocoa, and baking powder and add the chopped chocolate. Mix well to form a soft dough.
Roll the mixture into 20 small balls and divide between the baking trays, spacing well apart. Press each cookie down and top with a little crumble mix. Bake for 10-12 minutes until the crumble topping is golden, then remove from the oven and leave for 5 minutes before transferring to a cooling rack.