1
Saute chopped onion in hot oil in a large skillet over medium-high heat 5 minutes or until tender.
2
Add garlic, saute 1 minute more, then add beef and cook until no longer pink. Drain beef mixture and return to pan.
3
Stir in pasta sauce and 1/2 tsp salt; set aside.
4
Cook pasta in a large Dutch oven (follow package directions); drain and return to Dutch oven.
5
Melt butter in a heavy saucepan over low heat; whisk in flour until smooth. Cook, whisking constantly, for 1 minute. Then, gradually whisk in milk; cook over medium heat, whisking constantly, until mixture is thickened and bubbly.
6
Stir in Parmesan cheese, remaining 1/4 tsp salt and pepper. Pour sauce over pasta in Dutch oven, stirring until pasta is evely coated.
7
Transfer pasta mixture into lightly greased 13x9-inch baking dish. Top evenly with beef mixture; sprinkle evenly with mozzarella cheese.
8
Bake at 350 degrees for 20-25 minutes or until cheese is melted; let stand 10 minutes before serving.