Preheat oven to 225 degrees. Place egg whites and cream of tartar in a clean bowl. Mix on medium-high speed with the whisk attachment until foam begins to form on the egg whites. While the mixer continues on medim-high speed, slowly add the sugar and whisk until stiff peaks form, around 8-10 minutes. Add vanilla and ½ cup chopped pistachios and mix on high for 10 seconds to combine.

Put batter in piping bag and dollop in to kisses on 2 baking sheets lined with parchment paper. Leave 1-2 inches of space between meringues. Sprinkle tops with remaining ½ cup chopped pistachios.

Bake for 2 hours. Once cooled, store meringues in an airtight container until ready to serve. For plain meringues, follow the recipe above but leave out the pistachios.