I prefer to use a double boiler for this recipe. I make my own by adding a couple of inches of water in a saucepan and setting a glass bowl over the top.
Put the chopped dark and milk chocolate in a heat-proof bowl and cover it with the cream. Set the bowl over the saucepan and bring to a high simmer or low boil.
Put the chocolate mixture into the refrigerator for at least 1 hour or until the mixture is hard but not solid. If you press it with your finger it will dent but not push through.