Rainbow Confetti Marshmallow Popcorn Treats

1.   Grease a 9-by-13-inch baking pan with cooking spray.  
2. Melt the butter in a large stock pot over medium-low heat. Carefully stir in the vanilla extract (it will spatter), then add the marshmallows and cook, stirring, until smooth, about 5 minutes. Stir in the popcorn and 1/4 cup of the sprinkles until the popcorn is well coated, then immediately pour the mixture into the prepared baking dish, pressing it firmly into an even layer. Sprinkle the remaining 1/4 cup sprinkles on top.  
3. Let the treats sit for 20 minutes then slice into squares or bars and serve.

Cook’s Note

You can use microwave popcorn (plain or lightly salted, but not buttered), or pop your own. You'll need about 1/2 cup kernels to yield 10 cups popcorn. Lightly salted works best in terms of flavor.