Bring a large pot of water to a boil and cook the macaroni for 6 minutes. Drain and add to a 6 quart slow cooker.
Add the grated cheddar and butter to a microwave safe bowl and heat in 30 second increments, stirring each time, until melted. Pour the cheese mixture over the macaroni.
Add the cream cheese, cheddar soup, sour cream, milk, salt, pepper, and mustard powder to the slow cooker and stir well to coat the noodles.
Cover and cook on low for 3 hours.
Stir well before serving.
Video
Notes
You'll find the condensed cheese soup near the rest of the condensed soups in the grocery store.