Cook the Noodles: Bring a large pot of salted water to a boil. Add the lasagna noodles and cook until al dente, about 8–10 minutes. Drain and set aside.

Sauté the Onion: In a skillet, heat the olive oil over medium heat. Add the diced onion and sauté until softened, about 4–5 minutes. Add minced garlic and cook until fragrant, about 1 minute.

Brown the Beef: Add ground beef to the skillet, stirring until browned and cooked through, about 6–8 minutes. Season with salt, pepper, and Italian seasoning, then mix in the marinara sauce and simmer.

Prepare the Cheese Mixture: In a medium bowl, combine softened cream cheese, ricotta cheese, and egg. Stir until smooth, then fold in half the grated Parmesan.

Layer the Ingredients: In a baking dish, layer the meat sauce, noodles, half of the cheese mixture, and a third of the mozzarella. Repeat, finishing with sauce and remaining mozzarella.

Bake the Lasagna: Cover with foil and bake at 375°F (190°C) for 30 minutes. Remove foil and bake for an additional 15 minutes until cheese is bubbly.

Rest and Serve: Let the lasagna rest for 10–15 minutes before slicing.