How to Make It
Boil the macaroni in a 2 quart saucepan in plenty of water until tender, about 7 minutes. 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 sour cream, soup, salt, milk, mustard and pepper and stir well. Then add drained macaroni and stir again. Set the slow cooker on high setting and cook for 3 hours, stirring occasionally.