- 2 tablespoons unsalted butter, plus more for the dish
- 1/2 cup popcorn kernels or one 3.5-ounce package plain microwave popcorn
- 1 10-ounce bag marshmallows
- Butter a 9-by-13-inch baking dish. Pop the popcorn according to the package directions.
- Melt the butter and marshmallows in a large saucepan over medium-low heat, stirring until smooth, 5 to 7 minutes.
- Fold in the popcorn until coated. Press into the prepared dish and let sit for 10 minutes before cutting into 24 bars.