01 - Blend milk and spinach leaves until completely smooth and vibrant green. Strain through fine mesh sieve into medium saucepan, pressing to extract all liquid.
02 - Add heavy cream, sugar, and salt to saucepan. Heat over medium heat, stirring constantly until mixture steams but does not boil.
03 - Whisk egg yolks in separate bowl. Slowly pour 1 cup hot cream mixture into yolks while whisking continuously to temper eggs.
04 - Return yolk mixture to saucepan. Cook over medium-low heat, stirring constantly, until custard thickens enough to coat back of spoon (170-175°F).
05 - Remove from heat. Stir in peppermint extract, vanilla extract, and green food coloring if using.
06 - Pour custard through fine mesh sieve into clean bowl. Cool to room temperature, cover, and refrigerate at least 4 hours or overnight.
07 - Churn chilled custard in ice cream maker according to manufacturer instructions. Add chocolate chips during final 2 minutes of churning.
08 - Transfer churned ice cream to freezer-safe container with lid. Freeze at least 2 hours until firm before serving.