Preheat oven to 350°F. Line or grease an 8×8-inch baking pan.

In a bowl, combine brownie mix, melted butter, milk, egg, brown sugar, and espresso powder. Mix until smooth.

Pour batter into prepared pan and spread evenly.

Warm peanut butter slightly (10–15 seconds in the microwave) so it’s easy to drizzle.

Drop spoonfuls of peanut butter over the brownie batter. Use a knife or toothpick to gently swirl it into the top.

Bake for 18–22 minutes, until the center is just set and a toothpick comes out with a few moist crumbs.

Let cool before slicing for clean edges. Enjoy!