Cook macaroni in a pot of boiling water for 6 minutes and drain. You undercook the macaroni slightly so it doesn't get mushy after cooking in the crock pot.

In a sauce pan, melt butter over medium heat. Add cheese and cheddar cheese soup. Stir until the cheese is melted and mixture is smooth.

Spray your slow cooker and add your cooked macaroni along with the cheese mixture, sour cream, salt, milk, dry mustard, and pepper. Stir until well combined and coated.

Cook on low for 2-21/2 hours until hot, stirring occasionally. Serves 4.