Prepare the Peanut Butter Dough

1. Cream Butter and Sugars: In a large bowl, cream together the softened butter, peanut butter, granulated sugar, and brown sugar until light and fluffy.
2. Add Egg and Vanilla: Beat in the egg and vanilla extract until well combined.
3. Combine Dry Ingredients: In a separate bowl, whisk together flour, baking powder, baking soda, and salt.
4. Mix into Wet Ingredients: Gradually add the dry ingredients to the peanut butter mixture, mixing until just combined. Set aside.

Prepare the Brownie Dough

1. Combine Butter and Sugars: In a medium bowl, whisk together the melted butter, granulated sugar, and brown sugar until smooth.
2. Add Egg and Vanilla: Stir in the egg and vanilla extract until well incorporated.
3. Mix in Dry Ingredients: In a separate bowl, whisk together flour, cocoa powder, baking soda, and salt. Gradually add to the wet ingredients and mix until smooth.

Create the Swirl and Bake

1. Preheat Oven: Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper.
2. Swirl Doughs Together: Take 1 tablespoon of each dough (peanut butter and brownie) and gently press them together. Roll them into a ball, being careful not to overmix to maintain the swirl.
3. Arrange on Baking Sheet: Place the cookie dough balls on the prepared baking sheet, leaving space between each cookie.
4. Bake: Bake in the preheated oven for 12-15 minutes or until the edges are set. The centers may still look slightly undercooked.
5. Cool: Allow the cookies to cool on the baking sheet for 5 minutes, then transfer to a wire rack to cool completely.