Preheat your oven to 375°F. Line rimmed baking sheets with unbleached parchment and set them aside.

In a large bowl, place the flour blend, xanthan gum, baking soda, salt and granulated sugar, and whisk to combine well. Add the brown sugar, and whisk to combine once more, working to break up any lumps in the brown sugar. Place the butter and peanut butter in a small saucepan over medium heat until melted and smooth. Create a well in the center of the dry ingredients, add the butter and peanut butter mixture. Mix to combine. Add the egg and vanilla, and mix again to combine. The dough will come together and be thick.

Divide the dough into 21 balls of approximately equal size (each a bit more than 1-inch in diameter). Roll the balls in the (optional) coarse sugar, pressing gently on all sides to make sure that the sugar adheres in a single layer to the cookie dough. Place about 2-inches apart on the prepared baking sheets (they’ll spread a bit during baking). Place in the center of the preheated oven and bake for 11 minutes, or until the balls of dough have flattened into thick disks and the cookies have begun to take on a slightly crackled appearance.

Remove the cookies from the oven and immediately press one unwrapped chocolate kiss in the center of each just-baked cookie, about halfway to the center of the cookie. Allow to cool on the baking sheet until firm (about 10 minutes) before transferring to a wire rack to cool completely. The chocolate kisses will firm up again as the cookies cool.