Preheat the oven to 300°F. Line a large baking sheet with parchment paper and set aside.
Put about 1 ¼ cup pistachio nuts in a food processor, and grind them until small crumbs. Scoop out 1 cup of ground pistachios.
In a large bowl, add 1 cup ground pistachios, 1 ¼ cup almond flour, ⅔ cup granulated sugar, ¼ tsp salt, and mix everything together.
In a separate bowl, add 2 large egg whites. Using a hand mixer or stand mixer with a whisk attachment, whisk the egg whites until stiff peaks.
Add the beaten egg whites to the dry ingredients and fold it in. It might seem stiff at first, but just keep mixing until everything is well combined.
Using a 1 ½ tbsp ice cream scoop or just a regular spoon, scoop out the cookie mixture and roll it into a small ball. Then roll it into powdered sugar to cover from all sides.
Place on a baking sheet with parchment paper, leaving 1-1 ½ inches in between the cookies.
Bake at 300°F for about 30-35 minutes. When done, take them out of the oven and let sit on the baking sheet for about 10-15 minutes to set, then transfer to a wire rack to cool off completely.