Slowly melt the butter in a saucepan with the chocolate. Once liquid, remove from the heat and stir in the cocoa. Add the marshmallow flavouring. Place the biscuits in a freezer bag. Crush with a pastry roller until crumbly. Fold the crumbs into the chocolate mixture. Leave to cool well. Finally, add the colourful coated peanuts. Lightly grease a baking tin (approx. 20x20 cm) and line with baking paper. Pour in the chocolate mixture and smooth it down. Place some more of the coated peanuts on top and press them in lightly. Leave to cool in the freezer for at least one hour.