01 - In a medium saucepan over medium heat, combine the heavy cream, whole milk, and half of the granulated sugar. Heat until just simmering, stirring occasionally, being careful not to boil.
02 - In a separate bowl, whisk the egg yolks with the remaining sugar until the mixture is pale and slightly thickened.
03 - Slowly pour about 1 cup of the hot milk mixture into the egg yolks, whisking constantly to prevent curdling.
04 - Return the tempered egg mixture to the saucepan. Cook over low heat, stirring constantly with a wooden spoon until the custard thickens and coats the back of the spoon, reaching 170–175°F (77–80°C). Avoid boiling.
05 - Remove from heat and immediately fold in the chopped bittersweet chocolate. Stir until fully melted and the mixture is smooth.
06 - Incorporate the mint extract, vanilla extract, and optional food coloring into the custard mixture.
07 - Pass the custard through a fine-mesh sieve into a clean bowl. Allow to cool to room temperature, then cover and refrigerate for at least 2 hours or overnight for best results.
08 - Process the chilled mixture in an ice cream maker following the manufacturer’s instructions. Add mini chocolate chips or chopped chocolate during the last minute of churning if desired.
09 - Transfer the churned ice cream to a lidded freezer-safe container and freeze for at least 2 hours until firm.