Preheat oven to 350ยบ F. Spray an 8-inch baking dish with nonstick cooking spray or coat lightly with butter.
Prepare fudge brownies according to recipe instructions and spread into the prepared baking dish.
Stir together peanut butter and confectioners sugar in a small bowl. Drop large dollops evenly over the top of the brownie batter.
Swirl the peanut butter into the brownie batter with a skewer or a knife.
Bake 30 minutes or until the center of the brownies do not move when baking pan is moved or a toothpick inserted in the center comes out with some brownie clinging to it but not liquid.
Remove from the oven and allow to cool completely before slicing.