1. In a small saucepan over medium heat, warm 2 cups of the heavy cream until beginning to steam. Remove from heat, add all of mint leaves, cover and steep for 2 hours. After 2 hours, pour the cream through a strainer, discarding the leaves and refrigerating the cream until cold.
2. Place 1 oz of the chopped chocolate in a heat-safe bowl. In a small saucepan, heat the remaining 1/4 cup heavy cream until beginning to steam. Remove from heat, and pour over the chopped chocolate. Allow the mixture to sit for a full minute before stirring with a spoon until all of the chocolate is melted and combined with the cream. Allow the ganache to cool slightly before preparing the ice cream.
3. In the bowl of a stand mixer fitted with the whisk attachment, or using an electric mixer, beat the cold, steeped cream until stiff peaks begin to form. Using a spatula, fold in the can of condensed milk, along with the remaining 4 oz of chopped chocolate and food colouring (if using) until combined. Layer half of the ice cream mixture into a freezer-safe container (I always use a standard sized loaf pan). Drop half of the ganache by spoonfuls on top of the ice cream and swirl it around with a spoon. Repeat with the remaining ice cream and ganache.
4. Freeze the ice cream for 5-6 hours before serving.

Ice cream will continue to harden over time. It will keep in the freezer for up to 2 weeks. I usually like to transfer my ice cream after a day into a freezer-safe container with a lid.