If the chocolate isn't fully melting (that is, the heavy cream wasn't hot enough), you can heat the mixture in the microwave on 50% power for 20 seconds, then stir until the chocolate melts. Repeat if needed. If you're using a non-microwave safe bowl, heat the bowl on the stove over an inch of simmering water (in a saucepan just large enough so the bottom of the bowl isn't touching the water), stirring until the chocolate fully melts.