Preheat your oven to 350°F about 15 minutes before you plan to bake your cookies. Line rimmed baking sheets with unbleached parchment paper and set them aside.
In a large bowl, place the flour, xanthan gum, salt, baking soda and granulated sugar, and whisk to combine well.
Add the brown sugar, and whisk again to combine, working out any lumps in the brown sugar. If you are finding many lumps, try using the tines of a fork to break up any stubborn ones.
Create a well in the center of the dry ingredients, and add the butter, eggs, and vanilla. First, mix the wet ingredients together, then stir to slowly incorporate in the dry ingredients a bit at a time until well-combined.
Add 12 ounces of chocolate chips and mix until evenly distributed throughout the cookie dough. The cookie dough will be thick but not stiff. Add more chocolate chips if you like, and mix thoroughly.
Divide the cookie dough into 21 portions (or 24 if you’ve used all 16 ounces of chips), and roll each tightly into a ball about 1 1/2 inches in diameter (and about 50 grams each).
Press each of the balls of dough into a disk about 1/2-inch thick and place about 2 inches apart on the prepared baking sheets.
As you’re rolling the dough, add a few more chocolate chips to each ball, if desired, and roll them into the dough.
To ensure the thickest cookies with the best flavor and color, cover the dough on the baking sheet and refrigerate the shaped cookie dough for at least 12 hours and up to 5 days.
Remove the chilled dough from the refrigerator and place the baking sheets, one at a time, in the center of the preheated oven.
Bake until the cookies are golden brown around the edges, light golden brown all over and set in the center (about 12 minutes).
Remove from the oven and allow the cookies to cool on the baking sheet for about 5 minutes or until firm before transferring to a wire rack to cool completely.