Cool fresh mint leaves and peppermint extract give this recipe a more invigorating flavor not found in most versions of mint ice cream. The crisp herbaceous flavor of fresh mint combined with the cooling intensity of peppermint extract makes an ice cream that highlights all the best parts of the herb. Stirring in a generous amount of chopped bittersweet chocolate adds that classic speckled look to the beloved mint chip flavor.
Combine the heavy cream, milk, peppermint extract, vanilla, salt and food coloring if using in a medium pot over medium heat and cook just until small bubbles start forming around the edge of the pot, 7 to 9 minutes. Immediately remove from the heat, add the mint leaves and set aside to steep at room temperature for 30 minutes.
Meanwhile, whisk the egg yolks and sugar in a large, heatproof mixing bowl until ribbons form and the mixture is pale yellow, about 2 minutes. Strain the milk mixture into the egg yolk mixture through a fine-mesh sieve. Whisk until the egg yolks are completely incorporated.
Pour the mixture back into the same pot as the cream-milk mixture (do not wash the bowl). Cook over medium-low heat, stirring constantly, until the mixture is very creamy and thick enough to coat the back of a spoon and an instant-read thermometer registers between 170 and 180 degrees F, 6 to 8 minutes. Strain the mixture back into the bowl and cool at room temperature for 30 minutes. Cover tightly with plastic wrap and refrigerate until cold, at least 4 hours. (For faster chilling, set the bowl over another bowl of ice water and stir frequently until cold, changing the ice water as needed.)
Churn the mixture in an ice cream machine according to the manufacturer's instructions until it’s the texture of soft serve, 20 to 30 minutes for most models. Add the chocolate, reserving 1/4 cup for garnish, and continue churning just until incorporated, 5 to 10 seconds. Quickly transfer the ice cream to a chilled 9-by-5-inch loaf pan (a metal one will help keep the chill). Sprinkle the reserved chocolate on top of the ice cream and freeze for at least 1 hour before serving.
For the best texture, freeze the bowl of the ice cream maker for at least 12 hours before churning.
The ice cream can be stored in the freezer for up to 2 weeks.