In a mixing bowl, beat the peanut butter, softened butter, and brown sugar until the mixture is light and fluffy. Add the egg and vanilla extract, and mix until fully incorporated. In a separate bowl, whisk together the flour, baking soda, and salt. Gradually add this dry mixture to the wet ingredients, stirring until just combined.

In another bowl, whisk the melted butter and sugar together until smooth. Add the cocoa powder and mix well. Then beat in the egg and vanilla extract until the batter is glossy. Fold in the flour, baking powder, salt, and chocolate chips, mixing until there are no dry streaks.

Refrigerate both doughs for 30 minutes to make them easier to handle.

Scoop 1-2 tablespoon portions of each dough and place them side by side on a parchment-lined baking sheet. Use a toothpick or skewer to gently swirl the two doughs together, creating a marble pattern.

Preheat your oven to 350°F (175°C). Bake the cookies for 9-11 minutes, or until the tops are slightly crackly and the edges are set. The centers should still look soft.

Let the cookies cool on the baking sheet for 5-10 minutes before transferring them to a wire rack to cool completely. Enjoy your perfectly swirled treats!