Cook spaghetti until just tender, not well done. Brown meat in 1 tablespoon butter. Add salt, pepper and tomato sauce.
In a bowl, combine cottage cheese, cream cheese, sour cream and onion.
Drain spaghetti. Place spaghetti in the bottom of a 2-quart casserole. Add 1/2 mixture of cheeses and 1/2 mixture of meat. Add remaining mixtures in same order with meat mixture on top. Pour 2 tablespoons melted butter over top and bake uncovered at 350 degrees F for 30 minutes.