In a large bowl, cream together softened butter and the brown sugar replacement with a hand mixer or in a stand mixer with a paddle attachment until light and fluffy. Add in vanilla extract and molasses, then mix cream together again until smooth, then add in the egg and mix until completely combined.
Sift in the almond flour, coconut flour, salt, gingerbread spices, baking soda, and ½ teaspoon of the xanthan gum. Mix the wet ingredients and the dry ingredients together until completely combined and no streaks remain
Separate the dough ball into two roughly equal pieces, then place them between two pieces of parchment paper or plastic wrap. Roll them to about ¼-inch thick, with a rolling pin, then transfer them to the fridge on a baking sheet to chill for at least 1 hour before making the shapes.
After the dough has chilled for at least 1 hour (up to 2 days), remove the plastic wrap and use cookie cutters to make your favorite festive shapes. Place on a parchment-lined baking sheet in a single layer, leaving space between the cookies, and freeze the raw cookie dough shapes for 15 minutes to prevent spreading in the oven. While the cookies are freezing, preheat the oven to 350°F. Repeat steps 5-7 until you have used up all of your cookie dough. You can re-roll the dough as many times as you want, but you may need to chill the dough again for 10-15 minutes to firm up if it begins to become hard to work with.
After the cookies have chilled in the freezer, place them in the preheated oven, and bake for 12-15 minutes for larger cookies, or 7-10 minutes for smaller cookies. Watch the cookies very closely to prevent burning. Allow them to cool on the baking sheet for 15 minutes before transferring them to a cooling rack to let them cool completely before frosting.
After the cookies have cooled, mix together the cream of tartar, heavy cream, and an egg white, then sift in the powdered sweetener. We like the icing to be a bit thicker for easier frosting, so if needed, add a tiny pinch of xanthan gum to thicken the icing. sing a piping bag and a small decorating tip, decorate your cookies. Have fun with it! We are definitely not expert decorators, but these still turned out very cute. Allow the icing to harden before stacking in a cookie box.
Store leftovers in an airtight container at room temperature for up to 3 days, then transfer to the fridge for another 3 days or so. To freeze, allow cookies to cool completely, then add the cookies to a freezer-safe container where they will keep for up to 1 year.