Heat your oven to 250 degrees. Line two sheet pans with parchment paper.
Add the aquafaba and cream of tartar to a very dry mixing bowl. Whisk with an electric beater on medium-high for 10 minutes, or until the mixture is voluminous and fluffy and holds stiff peaks. It should resemble whipped cream.
Stir in the sugar one tablespoon at a time, until the meringue is glossy.
Fold in the vanilla.
Drop tablespoons full of meringue onto the sheet pans. Sprinkle with chopped pistachios.
Bake for 90 minutes, or until the cookies are firm and dry.
Let cool completely before removing from the baking sheet.
Str cooked up to 1 week in a dry, airtight container.