Step 1

Grease a 9-inch square baking pan with softened butter. Melt 3 tablespoons butter in a large pot over medium heat. Add marshmallows; cook, stirring, until melted. Remove from heat.

Step 2

Stir in cereal and chosen mix-ins to combine. Press into prepared pan; let stand until firm, about 1 hour. Cut into squares and serve, or store in an airtight container at room temperature up to 3 days.