Preheat your oven to 350°F. Line a rimmed baking sheet with unbleached parchment paper and set it aside.

In a large bowl, place the flour blend, xanthan gum, baking powder, salt, confectioners’ sugar and granulated sugar, and whisk to combine well.

Add the butter, shortening, egg, and vanilla, and mix well to combine. The dough will seem crumbly until it comes together. It will be soft but should hold together well when squeezed.

Scoop the dough by about the heaping tablespoonful, roll each piece into a ball and press into a disk about 1/4 inch thick.

The cookie dough should seem tacky to the touch on all sides. If it appears to have dried out at all, moisten the outside of each piece with lukewarm water.

Press each disk carefully but firmly into coarse sugar, nonpareils or sprinkles until the decoration adheres to the dough all around. Place the disks of dough on the prepared baking sheet, about 1 inch apart from one another.

Place in the center of the preheated oven and bake for 10 minutes, or until the cookies are very lightly golden brown on the edges and set in the center.

Remove the baking sheet from the oven and allow the cookies to cool on the baking sheet for 5 minutes before transferring to a wire rack to cool completely.