Step 1

Line a 9x13-inch cake pan with parchment paper.

Step 2

Melt butter in a large pot over medium-low heat, cooking and stirring until butter is golden brown and smells nutty, 3 to 4 minutes. Stir marshmallows into brown butter and cook until melted, 2 to 3 minutes. Add bourbon and 1 teaspoon salt; stir until incorporated. Mix cake mix into marshmallow mixture until dissolved; remove pot from heat.

Step 3

Mix 1/2 the rice cereal and 1/2 the fruit-flavored cereal into marshmallow mixture until evenly coated. Mix remaining rice cereal and fruit-flavored cereal into marshmallow-cereal mixture; press into the prepared baking dish. Sprinkle sea salt over the top.