Step 1

Spray a 9x13-inch baking dish with cooking spray.

Step 2

Place cereal in a large heatproof bowl.

Step 3

Melt butter in a saucepan over medium-high heat. Stir brown sugar, cream, and corn syrup into butter; cook, stirring, until mixture becomes thick and syrupy, 7 minutes. Stir 2 teaspoons salt into butter mixture. Remove from heat and add marshmallows; stir until marshmallows are smooth and melted.

Step 4

Pour marshmallow mixture over rice cereal and stir. Transfer cereal mixture to prepared baking dish and press down with greased parchment paper. Sprinkle with 1/2 teaspoon sea salt; cool and cut into squares.