Preheat the oven to 350 degrees Fahrenheit.
Use a spice grinder or food processor to grind the pistachios into a fine flour.
In a bowl, combine the pistachio flour with the almond flour. Add sugar, eggs, and lemon zest. Mix to combine.
Break cookie dough into pieces a little bigger than a walnut shell. Coat hands in powdered sugar and rub on the outside of the cookie dough ball until the dough is covered in powdered sugar.
Place on an ungreased cookie sheet, leaving indents with your fingers on the dough.
Bake for about 15 minutes. The dough should still be soft, like marzipan. Bake for 18-22 minutes for a crunchier cookie.