1. In a medium bowl, sift together the rice, tapioca and teff flours, the baking soda, xanthan gum, cinnamon, pumpkin pie spice and salt. Whisk until well blended, and set aside.
2. In the bowl of a stand mixer cream the butter with the brown sugar on medium spped until the mixture is light, airy and pale tan, about 3 minutes. Add the egg and mix again on medium until incorporated, about 1 minute. Add the molasses, vanilla and grated ginger, then mix again at medium speed for another minute. Add half the dry ingredients and mix on low until incorporated. Add the second half of the dry ingredients and mix on low until the dough comes together in small clumps. (The dough will resemble thick brownie batter.) If the dough is too wet and not clumpy, add another tablespoon or two of rice flour. Shape the dough into a disk and place in a resealable plastic bag, removing excess air. Chill the dough in the refrigerator for about 2 hours.
3. Divide the dough in 3 equal portions. Refrigerate two portions while you work on the first. Place a sheet of parchment paper barely dusted with rice flour on your work surface then add the dough. Top the dough with another sheet of parchment that is lightly dusted with rice flour. Roll the dough out to a 1/8-inch thickness.Use a 2-inch round cookie cutter to cut out the cookies. Gather and re-roll the scraps. If the dough gets too warm, chill it again before rolling out the dough. Once a sheet pan is full of prepared cookies chill in the freezer for 15 minutes.
4. When ready to bake the cookies, adjust oven racks to the top and bottom thirds and preheat the oven to 350° F. Line two baking sheets with parchment.
5. Arrange the cookies on the prepared baking sheets about 1-inch apart and bake until the edges just begin to take on golden color, 8 to 10 minutes. Let the cookies cool for a minute on the cookie sheet, and then remove and place on a cooling rack to cool completely. Let the baking sheets cool completely between batches of cookies.
6. Repeat the process for the remaining dough portions.

Make the icing

1. In a small bowl combine the powdered sugar, vanilla extract and milk. Mix with a whisk until combined and no lumps remain. If necessary, add additional milk 1 teaspoon at a time until the icing reaches drizzling consistency. Transfer to a small plastic bag then cut a tiny hole in the corner when ready to ice the cookies.
2. Once completely cooled, decorate the cookies by drizzling with icing and a light sprinkle of sparkling sugar.