Make an ice-water bath; set aside. Using a sharp, heavy serrated knife or a chocolate chopper, finely chop the chocolate. It's important to chop it finely so that it melts quickly. Transfer to a medium bowl.
Bring heavy cream just to a boil, and pour over chopped chocolate. Stir until chocolate is melted and smooth.
Place the bowl over ice-water bath, and use a wooden spoon to stir the mixture vigorously until it reaches the desired thickness or consistency, about 5 minutes.