Add the granulated sugar, brown sugar, butter, and peanut butter to a large bowl and mix with your mixer until fully combined and creamy.
Mix in the egg and the molasses until fully combined.
In a medium bowl, combine the gluten-free flour, xanthan gum, baking soda, and baking powder.
Slowly pour the flour mixture into the batter and mix until fully combined; the cookie dough will resemble soft playdough.
Cover the cookie dough and refrigerate for 30 minutes.
Preheat oven to 375°F (190°C) and add 1/4 cup of granulated sugar to a small bowl for rolling the dough.
Scoop 1 tablespoon of dough and roll into a ball.
Roll the cookie dough ball in the granulated sugar and place onto a parchment-lined baking sheet.