Step 1

Preheat your oven to 350°F. Line large rimmed baking sheets with unbleached parchment paper and set them aside.

Step 2

In a small, heavy-bottom saucepan or a microwave-safe bowl, place the peanut butter and chopped butter. Place the saucepan over medium-low heat (or in the microwave for about 45 seconds on high) and stir until melted and smooth (about 2 minutes). Set aside to cool briefly.

Step 3

In a large bowl, place the flour, xanthan gum, baking soda, salt and granulated sugar, and whisk to combine well. Add the light brown sugar, and whisk again to combine, working out any lumps.

Step 4

Create a well in the center of the dry ingredients, and pour in the melted peanut butter and butter mixture. Mix to combine.

Step 5

Add the beaten eggs and vanilla, and mix again to combine well. The cookie dough will be soft and sticky.

Step 6

If the cookie dough is too sticky or soft to handle, or it feels particularly greasy, cover it and refrigerate it for 10 minutes or less. If you refrigerate it for too long, the dough will become crumbly.

Step 7

Pull or scoop off pieces of dough, each about 2 tablespoons in volume. Roll each piece of dough into a round between your palms.

Step 8

Press the ball into a disk about 1/2-inch thick and place about 1 1/2-inches apart on the prepared baking sheets.

Step 9

Wet the tines of a salad fork, dip in the optional extra sugar, and press the tines firmly into the top of each cookie. (See Recipe Notes)

Step 10

Wet the tines again, and press them again into the top of the same cookies in the opposite direction to make a crosshatch pattern.

Step 11

Place the cookies, one baking sheet at a time, in the center of the preheated oven and bake.

Step 12

For less crunchy cookies, bake until pale golden all over (about 15 minutes). For very crunchy cookies, bake until uniformly golden brown all over (about 18 minutes).

Step 13

Remove the baking sheet from the oven and allow to cool on the baking sheet until set (at least 5 minutes) before transferring to a wire rack to cool completely.

Step 14

The cookies will be very fragile when they first come out of the oven, so it is very important to let them sit on the baking sheet until they are set. They will crisp as they cool.