Line a 9 x 13-inch baking dish with aluminum foil, then spray the foil with cooking spray.
In a large pan, melt together the butter and 15 cups of marshmallows over low heat while stirring constantly. After the marshmallows are completely melted, add the vanilla.
10 tablespoons unsalted butter, 2 teaspoons pure vanilla extract
Next, stir in the cereal. When the cereal is combined, mix in the remaining 5 cups of miniature marshmallows.
12 cups Rice Krispies Cereal
Scoop out the warm rice krispie treats, and transfer to the prepared baking dish. Spray your hands or a spatula with cooking spray, and press the mixture into the dish to form an even layer.
Allow the treats to set for at least 30 minutes before cutting. Cut into 12 large squares, and save any extras in an airtight container for up to 3 days.
Notes
*The calories listed are an approximate and based on the serving size and ingredients listed.*Please see post for alternate cooking methods, ingredients, and storage information.