Step 1

Whisk flour blend, baking soda, salt, and xanthan gum together in medium bowl; set aside. Combine brown sugar, granulated sugar, and peanut butter in large bowl. Pour warm butter over sugar mixture and whisk to combine. Whisk in eggs and vanilla and continue to whisk until smooth. Stir in flour mixture with rubber spatula and mix until soft, homogeneous dough forms. Cover bowl with plastic wrap and let dough rest for 30 minutes. (Dough will be slightly shiny and soft.)

Step 2

Adjust oven rack to middle position and heat oven to 325 degrees. Line 2 baking sheets with parchment paper. Working with 2 generous tablespoons dough at a time, roll into balls and space 2 inches apart on prepared sheets. Using bottom of greased dry measuring cup, press each ball to ¾-inch thickness. Sprinkle tops evenly with peanuts.

Step 3

Bake cookies, 1 sheet at a time, until puffed and edges have begun to set but centers are still soft (cookies will look underdone), 12 to 14 minutes, rotating sheet halfway through baking. Let cookies cool on sheet for 5 minutes, then transfer to wire rack. Serve warm or at room temperature.