Cut the chocolate into pieces and melt in a double boiler or in the microwave.
Add half the hot heavy cream previously heated in a saucepan over medium heat and stir with a spatula or wooden spoon.
Add the other half of the cold heavy cream and mix again with a spatula to incorporate. Cover with plastic wrap and refrigerate overnight.
Place the cooled ganache in the bowl of your electric mixer and whip on medium speed for about 3 minutes until smooth and firm.
Use the whipped ganache to fill or decorate your cakes and cupcakes.