Peanut Butter Swirl Brownies (adapted)
1 boxed brownie mix for a 13x9 pan, prepared according to box directions
1 cup creamy peanut butter
1/3 cup sugar
4 tablespoons butter, melted
2 tablespoons all-purpose flour
1 teaspoon vanilla extract
1 large egg
Preheat oven to 350-degrees F. Line a 13x9 pan with aluminum foil, spraying the bottom of the foil-covered pan with cooking spray.
Prepare peanut butter swirl: using a stand mixer, beat peanut butter, sugar, butter, flour, vanilla, and egg until well blended.
Spread two-thirds of the prepared chocolate brownie batter into the bottom of the pan. Top with 6 large (or 12 small) dollops of peanut butter mixture. Top with remaining 1/3 of brownie batter. With tip of knife, cut and twist through mixtures to create swirled effect.
Bake brownie 30 to 35 minutes or until toothpick inserted 2 inches from edge comes out almost clean. Cool in pan on wire rack.
When cool, cut brownie lengthwise into 4 strips, then cut each strip crosswise into 6 pieces.