Boil the macaroni in a large pot until tender. Drain.
In a medium saucepan, mix butter and cheese. Stir until the cheese melts.
In a slow cooker, combine cheese/butter mixture and add the eggs, sour cream, soup, salt, milk, mustard and pepper and stir well. Then add drained macaroni and stir again. Set the slow cooker on low setting and cook for 3 hours.