1Preheat oven to 350 degrees F (175 degrees C). Grease a 9x13-inch baking dish.
2Beat brownie mix, vegetable oil, water, and 2 eggs in a bowl until batter is smooth.
3Whisk flour, baking powder, and salt together in a small bowl.
4Beat peanut butter, brown sugar, and 2 tablespoons butter together in another bowl with an electric mixer until light and creamy. Beat 1 egg and vanilla into peanut butter mixture until fluffy. Stir flour mixture into peanut butter mixture until just blended.
5Pour brownie batter in the prepared baking dish. Drop peanut butter mixture by small spoonfuls over the brownie batter.
6Bake brownies in the preheated oven until a toothpick inserted in the center of the brownies comes out clean, about 30 minutes; cool.
7Melt 1/4 cup butter in a large saucepan over medium heat; add marshmallows and stir until marshmallows are melted. Cook mixture until butter and marshmallow flavors are combined, about 2 minutes; remove from heat.
8Spread 1/3 the marshmallow mixture over the cooled brownies. Stir crispy rice cereal into remaining 2/3 the marshmallow mixture; press in an even layer on top of the brownies. Refrigerate until set, about 15 minutes; cut into squares.
Footnotes
Cook's Note:
You can 'marble' the brownies by running a knife through the spoonfuls of peanut butter mixture into the brownie batter.
Ingredients
16 servings
384 cals
1 (18 ounce) package fudge brownie mix
1/2 cup vegetable oil
1/4 cup water
2 eggs
1/3 cup flour
1/4 teaspoon baking powder
1/8 teaspoon salt
1/2 cup crunchy peanut butter
3/8 cup brown sugar
2 tablespoons butter, softened
1 egg
1/2 teaspoon vanilla extract
1/4 cup butter
4 cups miniature marshmallows
3 1/2 cups crispy rice cereal (such as Rice Krispies®)