In a mixing bowl, beat together peanut butter, softened butter, and brown sugar until light and fluffy—about 2–3 minutes.

Add the egg and vanilla extract; mix until well incorporated.

In another bowl, whisk together flour, baking soda, and salt. Gradually combine the dry ingredients with the wet mixture until just combined.

In a separate bowl, whisk together melted butter and white sugar until smooth.

Stir in cocoa powder, egg, and vanilla extract until blended.

Fold in flour, baking powder, and salt until no dry ingredients remain, then gently fold in chocolate chips.

Cover both bowls with plastic wrap and chill for about 30 minutes. Preheat oven to 350°F (175°C).

Line a baking sheet with parchment paper; scoop peanut butter and brownie dough, placing them next to each other.

Use a toothpick to gently swirl the doughs without overmixing.

Bake for 9–11 minutes; they should look slightly crackly on the tops.

Allow to cool on the baking sheet for 5–10 minutes before transferring to a wire rack.