Grease a 2-quart casserole or a 2-quart square baking dish; set aside. Cook noodles according to package directions; drain and set aside.

In a medium mixing bowl beat together the sour cream and cream cheese with an electric mixer on medium speed until smooth. Stir in milk and onion.

Meanwhile, in a large skillet cook beef until brown. Drain off fat. Stir tomato sauce, basil, sugar, garlic powder, salt, and pepper into skillet. Bring to boiling; reduce heat. Simmer, uncovered, for 5 minutes.

Preheat oven to 350°F.

In prepared casserole or baking dish, layer half of the noodles (about 2 cups), half of the meat mixture (about 1 1/2 cups), half of the cream cheese mixture (about 1 cup), and all of the spinach. Top with the remaining meat mixture and noodles. Cover and chill remaining cream cheese mixture until needed.

Cover casserole or baking dish with lightly greased foil. Bake in 350°F oven about 45 minutes or until heated through. Uncover; spread with remaining cream cheese mixture. Sprinkle with the cheddar cheese. Bake, uncovered, about 10 minutes more or until cheese is melted. Let stand for 10 minutes before serving.