Mix ingredients: In a medium size bowl, stir together the almond flour, tapioca starch, sugar, cream of tartar, baking soda and salt. Add the melted butter, egg and vanilla extract to the bowl. Stir until the ingredients are incorporated. Place in the fridge for 30 minutes to chill which will give the dough a chance to firm up and be easier to handle.
Preheat oven: Once you are ready to bake, preheat your oven to 325°F (162°C) and line two baking sheets with parchment paper.
Shape cookies: Each cookie uses 1 ½ teaspoons of dough. (The easiest way to portion out the dough is to use a cookie scoop or a tablespoon to scoop out a portion of dough and then use a butter knife to cut the portion in half.) Roll each portion into a ball and then use your finger to press the ball down into a disc shape. Place them on the cookie sheet 2 inches apart.
Bake: Bake the cookies for 20 minutes, turning halfway through the baking time to ensure they bake evenly. They will spread slightly and be golden brown when they are done. Transfer the baked cookies to a cooling rack to cool