Preheat the oven to 375°F (190°C). Grease a 9×13-inch baking dish with cooking spray or butter.

Heat a large skillet or pot over medium. Add the ground beef, Italian sausage, and diced onion. Cook, breaking up the meat, until browned and cooked through (about 7–10 minutes). Drain excess grease.

Stir in the minced garlic and cook 30–60 seconds until fragrant.

Add the marinara sauce and crushed tomatoes. Season with Italian seasoning, salt, pepper, and sugar if using. Reduce heat and simmer gently for 10–15 minutes, stirring occasionally. Taste and adjust seasoning.

Meanwhile, make the cheese mixture: in a large bowl combine ricotta, softened cream cheese, grated Parmesan, the egg, and parsley. Stir until smooth. Fold in 1 cup of the shredded mozzarella.

Cook the lasagna noodles according to package directions until al dente, then drain and lay them flat on a sheet of foil or lightly oiled tray to prevent sticking.

To assemble: spread a thin layer of the meat sauce across the bottom of the prepared baking dish. Lay 3 noodles over the sauce, slightly overlapping. Spread a generous layer of the cheese mixture over the noodles, then spoon on a layer of meat sauce. Sprinkle a handful of shredded mozzarella.

Repeat layers (noodles → cheese mixture → meat sauce → mozzarella) until ingredients are used, finishing with a top layer of meat sauce and the remaining shredded mozzarella.

Cover the dish tightly with aluminum foil and bake for 25 minutes. Remove the foil and bake an additional 15–20 minutes, until the cheese is bubbly and golden on top.

Remove from oven and let the lasagna rest for 10–15 minutes before slicing to allow the layers to set. Garnish with extra parsley if desired and serve warm.