Bake Sale Trifecta Bars

INGREDIENTS

Brownie Layer:

1 stick

unsalted butter, at room temperature, plus more for the pan

1 cup

granulated sugar

1/3 cup

packed light brown sugar

large eggs

2 tsp

pure vanilla extract

3/4 cup

all-purpose flour

1/2 cup

unsweetened cocoa powder

1/4 tsp

salt

Cookie Layer:

1 stick

unsalted butter, at room temperature

3/4 cup

packed light brown sugar

2 tbsp

granulated sugar

large egg

1 tsp

pure vanilla extract

1 1/2 cups

all-purpose flour

1/2 tsp

baking soda

1/2 tsp

salt

1 cup

chocolate chips

Cereal Treat Layer:

3 tbsp

unsalted butter, plus more for your hands

10 -ounce bag mini marshmallows

3 cups

crispy rice cereal