1 (7 ounce) box ready-cut spaghetti
2 tablespoons butter
1 (8 ounce) carton sour cream
1 cup shredded cheddar cheese
1 (8 ounce) package Monterey Jack cheese, divided
1 (12 ounce) package frozen, chopped spinach, thawed, very well drained
1 (6 ounce) can cheddar french-fried onions

Cook spaghetti according to package directions, drain and stir in butter until it melts. In large bowl, combine sour cream, cheddar cheese, half Monterey Jack cheese, spinach and half can onions. Fold into spaghetti and spoon into sprayed slow cooker.

Cover and cook on LOW for 2 to 4 hours.

When ready to serve, sprinkle remaining Jack Cheese and fried onion rings over top.