FOR THE COOKIES:
1 3⁄4 cups sugar
1 1⁄4 cups quinoa flour
1 1⁄4 cups white rice flour, plus more for dusting
1 teaspoon sea salt or kosher salt
1 1⁄2 teaspoons xanthan gum
1⁄2 teaspoon baking soda
1⁄4 cup arrowroot
1 cup unrefined coconut oil, melted
4 tablespoons pure vanilla extract
1⁄3 cup ice water
FOR THE FONDANT (OPTIONAL):
Cornstarch, for dusting
1 pound fondant (Geoffrey prefers Satin Ice Fondant brand at satinice.com)
1 recipe Royal Icing
Preheat the oven to 325°F. Make the cookies: In the bowl of a stand mixer fitted with the paddle attachment, combine the sugar, quinoa flour, white rice flour, salt, xanthan gum, baking soda, and arrowroot. Mix on low speed until blended. On medium-low speed, mix in the melted coconut oil until combined. Add the egg and vanilla, mix until incorporated, then add the water and mix to combine.
Scrape half the dough onto a piece of plastic wrap and flatten with the palm of your hand to a 1-inch-thick round, making sure the edge is smoothed. Wrap in the plastic wrap and repeat with the remaining dough. Refrigerate for at least 1 hour.
Line 2 large baking sheets with parchment paper. Remove the dough from the fridge and let it soften for a few minutes.
Lightly dust a clean work surface with rice flour. Using a rolling pin, roll out the dough to about 1⁄4 inch thick, adding more rice flour as needed to prevent sticking.
Cut out cookie shapes with cookie cutters of choice, place 1 inch apart on the prepared cookie sheets, and bake until slightly golden, 12 to 14 minutes, rotating the sheets halfway through to evenly distribute the heat. Cool for at least 1 hour.
If decorating with fondant: Lightly dust a clean work surface with cornstarch. Working in stages to prevent drying out, roll out the fondant 1⁄8 inch thick, then use cookie cutters to cut out shapes. Using a small rounded pastry brush, paint the top of each sugar cookie with a very light coat of cold water. Place the fondant shape on the cookie and gently press down, then round the fondant edges with your finger. Let the cookies and fondant dry on the cookie sheet for at least 1 hour before the next step of adding royal icing.
Fill a pastry bag with royal icing, fit it with your preferred pastry tip, and decorate as desired. Let dry for 3 hours to assure the icing has set.