01 - Combine heavy cream and milk in a medium saucepan. Heat over medium heat until just steaming, avoiding boiling.
02 - Whisk egg yolks and sugar in a separate bowl until pale and thickened.
03 - Slowly pour approximately 1/2 cup hot cream mixture into egg yolks while whisking continuously to temper.
04 - Return egg mixture to saucepan. Cook over low heat, stirring constantly, until custard thickens and coats the back of a spoon (about 170°F).
05 - Remove from heat. Stir in mint extract, vanilla extract, salt, and green food coloring if using.
06 - Pour custard through a fine-mesh sieve into a clean bowl. Cool to room temperature, then cover and refrigerate for at least 4 hours or overnight.
07 - Churn the chilled mixture in your ice cream maker according to manufacturer instructions.
08 - During the final 2 minutes of churning, add chocolate chips or chopped chocolate.
09 - Transfer ice cream to a lidded freezer-safe container. Freeze for at least 2 hours until firm.
10 - Scoop into bowls and serve immediately.