2  cup  uncooked elbow macaroni (an 8 ounce box isn't quite 2 cups)
2 1/2  cup  (about 10-ounces) grated sharp Cheddar cheese
3 eggs, beaten
1/2  cup  sour cream
1 (10 3/4-ounce) can condensed Cheddar cheese soup
4  tablespoon  (1/2 stick) butter, cut into pieces
1/2  teaspoon  salt
1  cup  whole milk
1/2  teaspoon  dry mustard
1/2  teaspoon  pepper

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 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, stirring occasionally.