• Preheat your oven to 325°F. Line rimmed baking sheets with unbleached parchment paper and set them aside.

Make the cookie dough.

• In a large bowl, place the almond flour, tapioca starch, optional xanthan gum, baking powder, salt, and granulated sugar, and whisk to combine well.
• Add the butter, egg, and vanilla, and mix to combine. Add at least 1/2 teaspoonful of water, and mix it into the dough.
• If the dough has any spots that seem dry or crumbly, add more water by the half-teaspoonful and mix to combine.
• Using clean hands, knead the dough together until it forms a ball. It will be thick and relatively stiff. Sprinkle in more water as necessary to bring the dough together.
• Divide the dough in half and set one half aside, draped with a tea towel to prevent it from drying out.

Shape the cookies.

• Place the first half of the dough on a lightly floured surface, sprinkle the top lightly with more tapioca flour, and roll it out a bit less than 1/3-inch thick.
• Move the dough often to prevent it from sticking, sprinkling lightly with more tapioca flour as necessary.
• Using a 2 1/2-inch round cookie cutter or other shapes, cut out shapes of dough. Pull off the excess cookie dough away from the shapes you've cut.
• Place the cutout shapes of dough about 1-inch apart from one another on the prepared baking sheets. The cookies won't spread during baking, so just make sure they're not touching.
• Gather and reroll the scraps, and repeat the process with all the remaining dough until it’s all been used.

Bake the cookies.

• One at a time, place the baking sheets in the center of the preheated oven and bake until just set in the center (about 10 minutes).
• The edges of some of the cookies may brown slightly, but take them out before there is any significant browning.
• Remove the cookies from the oven and allow them to cool on the baking sheet for about 5 minutes or until stable before transferring them to a wire rack to cool completely.

Prepare any icing

• Once the cookies are cool, you can ice, glaze, or frost them them as you would any other sugar cookie.