1. Cut 185g unsalted butter into smallish cubes and tip into a medium bowl. Break 185g best dark chocolate into small pieces and drop into the bowl. Fill a small saucepan about a quarter full with hot water, then sit the bowl on top so it rests on the rim of the pan, not touching the water. Put over a low heat until the butter and chocolate have melted, stirring occasionally to mix them. Now remove the bowl from the pan. Alternatively, cover the bowl loosely with cling film and put in the microwave for 2 minutes on High. Leave the melted mixture to cool to room temperature.