Begin the ganache a day ahead to allow time for the fresh mint leaves to infuse their flavor into the cream. Need a shortcut? Skip the fresh mint infusion and make plain ganache frosting. Flavor it with a drop or two of mint oil or some peppermint extract, to taste.
Adapted from “Chewy Gooey Crispy Crunchy Melt-in-your-Mouth Cookies” by Alice Medrich.
Stir the chopped mint into the cream. Cover and refrigerator for at least 8 hours and up to 12 hours. Strain the cream into a small saucepan, pressing gently on the leaves to drain out as much cream as you can. Discard the mint leaves. Heat the cream to a simmer. Meanwhile, put the chocolate into a clean bowl. Pour the hot cream over the chocolate and stir until the chocolate is completely melted and smooth. Cool; cover with plastic wrap and refrigerate for at least 4 hours and up to 2 days.
To use, remove the ganache from the refrigerator and check its consistency. If it is smooth and creamy, it can be used right away. If the ganache is too fluid or soft to spread without dripping, stir it vigorously with a rubber spatula for a few seconds (it will appear to soften; don’t worry) and return to the fridge for a few minutes, then check again.