Step 1: Prepare the Peanut Butter Dough

1. In a large bowl, beat together the peanut butter, softened butter, and brown sugar until light and fluffy.
2. Add the egg and vanilla extract, mixing until smooth.
3. In a separate bowl, whisk together the flour, baking soda, and salt. Gradually mix the dry ingredients into the wet ingredients until just combined. Set aside.

Step 2: Prepare the Brownie Dough

1. In another bowl, beat the melted butter and white sugar until smooth.
2. Add the egg and cocoa powder, mixing until well incorporated.
3. Stir in the flour, baking powder, chocolate chips, and salt until a fudgy dough forms.

Step 3: Swirl the Doughs

1. Scoop 1 tablespoon of peanut butter dough and 1 tablespoon of brownie dough. Roll each into a ball and place them side by side on a lined baking sheet.
2. Gently press the dough balls together and use a toothpick or knife to create a swirled design.
3. Repeat with the remaining dough, spacing cookies about 2 inches apart.

Step 4: Bake to Perfection

1. Preheat your oven to 350°F (175°C).
2. Bake the cookies for 10-12 minutes, or until the edges are golden and the centers are just set.
3. Let the cookies cool on the baking sheet for 5 minutes, then transfer them to a wire rack to cool completely.