- Combine the butter and marshmallows in a 3- to 4-quart slow cooker.
- Cover and cook on LOW setting 1 hour. Add cake mix and stir until well blended. Stir in cereal, and half of the sprinkles if using, so it is completely coated with marshmallow mixture.
- Either drop the mixture by tablespoons onto wax paper or press into a baking dish – top with remaining sprinkles. Let it sit for 30 minutes (give or take), then enjoy! Store in an airtight container.