Make the Meat Sauce: In a large pan, heat olive oil over medium heat. Add the ground beef (or beef and sausage mix) and cook, breaking it up with a wooden spoon, until browned. Add chopped onion and crushed garlic, and cook until softened. Season with salt, pepper, oregano, and paprika.

Stir in tomato sauce, tomato paste, water (or stock), and bay leaves. Bring to a boil, then reduce heat and simmer uncovered for 40–60 minutes, stirring occasionally. Discard bay leaves and set aside.

Prepare the Béchamel Sauce: In a saucepan, melt butter over low heat. Add flour and whisk constantly for 1–2 minutes to form a smooth roux. Gradually pour in warm milk, whisking until the sauce thickens and becomes smooth. Stir in salt, pepper, nutmeg, and Parmesan cheese. Remove from heat.

Preheat Oven: Preheat oven to 350°F (180°C).

Assemble the Lasagna: Grease a 13x9 inch (32x22 cm) baking dish. Spread a thin layer of meat sauce on the bottom. Add a layer of no-boil noodles, followed by ⅓ of the meat sauce, ¼ of the béchamel sauce, and a sprinkle of mozzarella. Repeat the layering two more times. Finish with béchamel sauce and top with mozzarella and grated Parmesan.

Bake: Cover with foil sprayed with non-stick spray. Bake for 40 minutes, then remove foil and bake another 15–20 minutes until golden and bubbly.

Rest and Serve: Let the lasagna rest for 15–20 minutes before slicing and serving.