In a large pot, heat olive oil over medium heat. Add chopped onion and minced garlic, sauté until translucent. Add the beef shank, season with salt and pepper, and brown on all sides. Pour in enough water to cover the meat, bring to a boil, then reduce to a simmer and cover. Cook for about 2 hours until the meat is tender. Remove the meat, shred it, and set aside.

Prepare Bechamel Sauce

In a saucepan, melt butter over medium heat. Stir in flour and cook for 1-2 minutes until golden. Gradually whisk in milk, stirring constantly until the sauce thickens. Season with salt, pepper, and a pinch of nutmeg. Remove from heat and stir in ricotta cheese.

Assemble Lasagna

Preheat your oven to 375°F (190°C). In a baking dish, spread a layer of tomato sauce on the bottom. Place a layer of cooked lasagna noodles, followed by a layer of the shredded beef, then a layer of the ricotta béchamel, and a layer of mozzarella cheese. Repeat the layers, finishing with a layer of noodles topped with remaining tomato sauce, mozzarella, and parmesan cheese.

Bake the Lasagna

Cover the baking dish with aluminum foil and bake for 30 minutes. Remove the foil and bake for an additional 15-20 minutes until the top is golden and bubbly. Let it cool for 10 minutes before serving.