Preheat your oven to 325°F. Line rimmed baking sheets with unbleached parchment paper and set them aside.

In a large bowl, place the flour, xanthan gum, cornstarch, salt, baking soda, and granulated sugar, and whisk to combine well. Add the brown sugar, and whisk to combine again, working out any lumps. Create a well in the center of the dry ingredients and add the peanut butter, butter mixture, eggs, and vanilla, and mix to combine. The dough will be thick but very soft. Add the chocolate chips, reserving a few. Mix until the chips are evenly distributed throughout the dough.

Scoop the dough into portions about 1 1/2 tablespoons in volume. Roll each piece of dough into a ball and then flatten into a disk about 1/2-inch thick. Place on the prepared baking sheets at least 2 inches apart from one another, since the cookies will spread during baking. For slightly thicker cookies, chill the shaped dough until it’s mostly firm to the touch (about 10 minutes in the freezer).

Place the baking sheets, one at a time, in the center of the preheated oven and bake until set and lightly golden brown all over (about 15 minutes). Remove from the oven and allow to cool for at least 10 minutes on the baking sheet or until firm before transferring to a wire rack to cool completely.