Chop the chocolate into small pieces so it can easily melt when you pour the heavy cream over it in the next step. Place the chocolate into a heatproof bowl and set it aside.
Pour the heavy cream into a medium pan, add the orange zest and stir. Place the pan over medium heat. Let the mixture scald (the small bubbles occur around the edge of the pan-it is just before the boiling stage).
Remove the heavy cream from the heat and pour it over the chocolate. Wait for 1-2 minutes before stirring the mixture to allow the cream soften the chocolate.
Let the ganache cool at room temperature and then keep it in the fridge for 1 hour so it becomes firm. If you are in a hurry, you can fasten this process by placing the ganache in a shallow dish; this way it can cool faster.
