Over double boiler melt chopped chocolate until completely smooth and has no lumps, then stir in heavy whipping cream(from the fridge). It should be very thick and creamy so you could spread it on top the cake but also on sides without dripping. Use just 2/3 of the ganache and set the cake in the freezer for 5-10 minutes to harden the ganache. Take the cake from the freezer and reheat the rest of the ganache but this time it should be smooth (but not too thin) so you can pour it over the cake to make the smooth and shiny surface.
To keep the shine of the ganache let it cool at room temperature then store the cake in the fridge.
