Add the chocolate chips or the chopped chocolate slab to a large heatproof bowl, ideally in the bowl of a stand mixer.
Add the heavy cream to a small saucepan set over medium heat, and allow the cream to warm until just before boiling.
Pour the hot cream over the chocolate and allow the mixture to sit for about 2 minutes before stirring with a rubber spatula. Once stirred, all the chocolate should’ve melted and the mixture should have a smooth texture.
Place a piece of plastic wrap over the warm ganache mixture, and ensure the plastic makes contact with the surface of the chocolate mixture. Allow the ganache mixture to set for about 6 hours or overnight in the fridge.
Beat the ganache using a handheld or stand mixer fitted with a whisk attachment. Beat at medium-high speed for about 5 minutes until a stiff peak forms and the frosting is light and fluffy.
Fill a piping bag with the beaten ganache or use an offset spatula to decorate your cakes and cupcakes.