4 ounces process cheese (Velveeta), cubed, divided
2 tablespoons grated Parmesan cheese
Cook spaghetti according to package directions. Meanwhile, in a large skillet, cook beef and onion over medium heat until meat is no longer pink; drain. Add spaghetti sauce; bring to a boil. Reduce heat; simmer, uncovered, for 10 minutes. Drain spaghetti; stir into beef mixture. Set aside.
In a small saucepan, melt butter. Stir in flour and salt; gradually stir in milk and water. Bring to a boil; cook and stir until thickened and bubbly. Add 1/2 cup process cheese and Parmesan cheese; stir until melted.
Spread half of the spaghetti mixture into a greased 11x7-in. baking dish. Cover with cheese sauce; top with remaining spaghetti mixture and process cheese.
Bake, uncovered, at 350° for 25-30 minutes or until heated through.