Place all the ingredients for the base in the bowl of a food processor. Blend the mixture until the mixture takes on a sandy texture.
Place 48 gold petit four cases in sets of miniature tart tins or mini-muffin tins (each indent about 1 3/4-inches in diameter). Use 1 teaspoon of the base mixture to fill the bases of the petit four cases. Press the sandy mixture down into the cases as best you can to form a layer at the bottom of each paper case.
Place the milk chocolate and dark chocolate together into a heatproof bowl. Suspend the bowl over a pan of simmering water (the water should not touch the bottom of the bowl). Melt the chocolate gently while stirring. Spoon teaspoonfuls of the melted chocolate onto the top of each of the sandy bases of the petit four cases.
Decorate the tops of the chocolate covered peanut butter cups with either a gold button or gold star in the middle of each and transfer them to the fridge. Let them set in the fridge, for about 30 minutes.
To serve, arrange the chocolate peanut butter cups in their cases on a clean plate.
Recipe courtesy of Nigella Lawson from Nigella's Christmas Kitchen, 2007