To make the chocolate ganache, melt the chocolate in a heatproof bowl over a pan of gently simmering water, making sure the base of the bowl doesn’t touch the water, and stirring occasionally. In a separate small pan, heat the double cream and sugar until it is just about to boil, turn down the heat, stir in the coﬀee and rum. Remove from heat. Combine with the chocolate. Cover and cool, then put in the freezer for at least 30 minutes until it thickens.