Sauté onions and garlic in oil, add beef and salt, brown well. Stir in tomato sauce, simmer, and salt to taste.
In a separate pan, sauté onions, garlic and spinach until wilted. Off heat, mix with ricotta, then eggs and parmesan. Season to taste.
Cook noodles until slightly al dente.
Butter a 9x13 inch dish. Line bottom with noodles, letting ends hang over edges.
Layer: thin meat sauce, noodles, ⅓ meat sauce and ¼ mozzarella, noodles, ⅓ spinach mix. Repeat for 3 full layers.
Fold over noodles, top with sauce, sliced mozzarella and remaining parmesan.
Cover with foil and bake at 350°F for 20 minutes. Uncover and bake 15 minutes more until browned. Let it rest, slice and serve.
