Preheat the Oven: Set your oven to 350°F (175°C). Line a baking sheet with parchment paper or a silicone baking mat.
Cream the Butters and Sugar: In a large mixing bowl, use a hand mixer or stand mixer to beat the peanut butter, softened butter, and brown sugar together until light and fluffy (about 2 minutes).
Add Egg and Vanilla: Beat in the egg and vanilla extract until well incorporated.
Mix Dry Ingredients: In a separate bowl, whisk together the flour, baking soda, and salt.
Combine Wet and Dry: Gradually add the dry ingredients into the peanut butter mixture, mixing just until combined. Do not overmix.
Shape the Cookies: Scoop out tablespoon-sized portions of dough and roll them into balls. Place them 2 inches apart on the prepared baking sheet. Gently press each ball down slightly with your fingers or a fork.
Bake: Bake for 10–12 minutes, or until the edges are set and the tops look slightly underbaked — this helps keep them thick and chewy.
Cool: Let the cookies cool on the baking sheet for 5 minutes before transferring them to a wire rack to cool completely.