Preheat the oven to 325°F and line a baking sheet with parchment paper.
In a large bowl, whisk together the almond flour, oat flour, matcha powder, and salt.
Add the maple syrup and stir until no dry spots remain.
Mix the pistachios in, if using, until they’re evenly distributed. The dough will be crumbly.
Scoop dough by rounded tablespoons (about 21g dough per scoop), roll into balls, place the balls on the parchment-lined baking sheet, and flatten to ½ inch thick (about 2 inch diameter). If dough sticks to your hands, you can wet them slightly before handling the dough, or use the bottom of a glass or measuring cup to flatten the balls.
Bake the cookies for 12 minutes. Let them cool on the pan for 10 minutes before handling them.
Store leftovers in an airtight container at room temperature for up to a week, refrigerated for up to 10 days, or frozen for up to 2 months. The cookies might become slightly chewy after being stored, but will still be delicious.