01 - Combine heavy cream, milk, and half of the sugar in a medium saucepan. Heat over medium heat until steaming but not boiling.
02 - Whisk egg yolks with remaining sugar in a bowl until pale and slightly thickened.
03 - Gradually pour hot cream mixture into yolks while whisking constantly. Return mixture to saucepan.
04 - Cook over low heat, stirring constantly, until custard thickens enough to coat back of spoon (approximately 170°F). Do not boil.
05 - Remove from heat and stir in peppermint extract, vanilla extract, and salt.
06 - Blend custard with spinach leaves in blender until smooth if using natural color, or stir in green food coloring to desired shade.
07 - Strain mixture through fine-mesh sieve into clean bowl. Cool to room temperature, cover, and refrigerate at least 4 hours or until thoroughly chilled.
08 - Churn custard in ice cream maker according to manufacturer instructions. Add chocolate chips or chopped chocolate when almost finished.
09 - Transfer to freezer-safe container, cover, and freeze at least 2 hours or until firm.