Make the dough
Blitz 200g quadruple chocolate cookies to fine crumbs in a food processor. Break a 100g bar of dark chocolate into pieces, setting aside a few squares for decoration later. Melt the remaining chocolate in a bowl placed over a pan of barely simmering water, being careful not to let the bowl touch the water. Add the melted chocolate to the food processor and blitz until the mixture starts to clump together.