When cooled, un-mold the cake. It is easiest to pull the sides of the foil pan away from the cake and then flipping it onto a plate. Set un-molded cake aside; if you find it is still slightly warm, you can put it back in the refrigerator while you make the ganache. Put remaining chocolate in a small heat-safe bowl and set aside. In a small pot, heat heavy cream to a simmer, then pour it over chocolate. Let it sit 1 minute and then stir until the chocolate is fully melted, shiny, and smooth. (Use a rubber spatula or wooden spoon. Do not whisk: it will make the ganache full of bubbles.) This can be gently heated if chocolate does not completely melt from hot heavy cream; either over a low flame or by 20 second intervals in a microwave.