Knowing how to fix a broken ganache will save you from having to throw out an otherwise great batch.
There are two methods for fixing a broken ganache and both are simple when you know the process.
Fixing A Broken Ganache

Even the most stable ganache can break down during storage. Luckily you can bring it back with either of these two simple methods.
The first method works every time but takes a bit more care. The second technique is a bit of a shortcut but it also provides good results.
For the first method you will gradually beat the broken sauce with a small amount of heavy cream added.
Simply add no more than a quarter cup of heavy to your broken ganache and beat it together gradually.
Make sure your heavy cream is the same temperature as your ganache. And you will get best results if the temperature is a bit warm.
For the shortcut method you will pour a small amount of heavy cream directly on top of your broken ganache.
Pour your cream on the center and whisk starting at the surface of the ganache. Slowly whisk toward the outside to incorporate the cream completely.
Fixing Ganache That Breaks On The Stovetop

Fixing a ganache that breaks on the stove is quick and easy. Simply add more cream or sugar while still on the stove.
Keep in mind that adding cream or sugar to your broken ganache will change the thickness of your ganache. Further adjustments may need to be made to achieve the desired thickness.
Conclusion
Both of these methods are effective at fixing a broken ganache. But the first method should always be done if you have the time at it works every time.
Ensure that your temperatures are equal and just a bit warm works the best. To avoid breakdown, learn how to make the perfect chocolate ganache for next time.