I found this great quick and easy recipe on the Six Sisters web site. Here is my English translation of it.
225g butter melted 455g digestive biscuit crumbs (whiz biscuits in the food processor or place in a plastic bag and roll with rolling pin.)225g icing sugar225g + 4 tablespoons peanut butter100g milk chocolate100g dark chocolate
In a medium bowl, mix together the melted butter, digestive biscuit crumbs, icing sugar, a 225g peanut butter until well blended.Press evenly into the bottom of a 9×13 inch tin which has been lined with grease-proof paper and lightly greased with butter. For thicker bars use a smaller tin. In the microwave, melt the milk and dark chocolate with the peanut butter, stirring every 30 seconds until melted and smooth.Spread over the peanut butter layer.Refrigerate for at least one hour before cutting into squares.