Put mint leaves in a blender with 1 cup of the yogurt, and the sugar.
Blend until the mint is pureed and the sugar dissolved.
In a bowl, combine the pureed mixture with the remaining cup of yogurt and the pistachios.
Put into an ice cream maker and run for 30 minutes, or put into a freezer-safe bowl and freeze for about 4 hours, stirring vigorously every 30 minutes.
Serve immediately for soft serve, or, for a firmer frozen yogurt, freeze for 30 minutes before serving. Keep in freezer 2-3 months.