I made these for my sons and their friends yesterday. I probably don't need to tell you that 11 - 13 year old boys are weapons of mass consumption.
slightly adapted from Nigella Lawson's Express
125g unsalted butter, softened
200g dark chocolate, chopped
100g milk chocolate, chopped
200g shortbread biscuits, crushed to form uneven crumbs (some fine, some larger pieces)
100g white marshmallows
Icing sugar for dusting
Put the butter, chocolate and honey into a medium saucepan and melt them together over medium heat. Remove from the heat, take out 1/2 cup of this melted mixture and set it aside.
Add the crushed biscuits to the pan of melted chocolate and stir. Add the marshmallows and gently fold them through.
Spoon the mixture into a 17cm x 27cm disposable foil tray and level the top as well as you can with a spatula. Pour the reserved melted chocolate mixture over the top and spread to evenly cover the top.
Refrigerate for at least 2 hours or until set before cutting into pieces as big or as small as you like, Dust with icing sugar.