In a small bowl, combine the mascarpone, vanilla, and sweetener.
Mix gently but thoroughly with a fork or spatula, until well blended and smooth.
Roll by hand into 10 balls, about 1 inch in diameter. (if too soft to roll, chill 10 minutes and try again.)
Place the pistachios on a small plate and roll the truffles in them until completely coated.
Chill 30 minutes before serving.
Store in an airtight container in the refrigerator for up to one week or in the freezer for up to 3 months.
To make a savory version, omit the sweetener and vanilla. Stir in 1/2 teaspoon minced garlic and 1 tablespoon of chopped herbs. Parley, chives or basil would all be a good choice. You can also use a nut other than pistachio if it’s what you have on hand!