Prepare the Meat Sauce

1. Cook the Meat: In a large skillet, cook the ground beef or sausage over medium heat until browned. Drain excess fat.
2. Add Onion and Garlic: Add the chopped onion and garlic; cook until softened.
3. Combine Ingredients: Stir in the crushed tomatoes, tomato sauce, tomato paste, and Italian seasoning. Season with salt and pepper.
4. Simmer: Allow the sauce to simmer for 15-20 minutes, stirring occasionally, until it thickens.

Prepare the Ricotta Mixture

1. Combine Ingredients: In a medium bowl, mix the ricotta cheese, egg, grated Parmesan, and parsley until smooth. Set aside.

Assemble the Lasagna

1. Preheat Oven: Preheat your oven to 375°F (190°C).
2. Layer the Ingredients: Spread a thin layer of the meat sauce in the bottom of a 9×13-inch baking dish. Layer 4 lasagna noodles over the sauce. Add 1/3 of the meat sauce, 1/3 of the ricotta mixture, and 1/3 of the shredded mozzarella. Repeat layers two more times, ending with a final layer of mozzarella and Parmesan on top.
3. Cover and Bake: Cover the dish with aluminum foil and bake for 45 minutes. Remove the foil and bake for an additional 15 minutes until the cheese is golden and bubbly.
4. Let Rest: Remove from the oven and allow the lasagna to rest for 10 minutes before serving.