In a large skillet, heat olive oil over medium heat. Sauté chopped onion and minced garlic until softened, about 3-4 minutes. Add ground beef and Italian sausage, cooking until browned. Stir in crushed tomatoes, tomato paste, and tomato sauce. Simmer for 30 minutes.

Combine ricotta cheese, beaten egg, grated Parmesan cheese, and a pinch of salt and pepper in a mixing bowl. Stir until smooth and creamy. Set aside.

Bring a large pot of salted water to a boil, then add lasagna noodles. Cook for about 8-10 minutes until al dente. Drain and rinse briefly with cold water. Lay noodles flat on a towel.

In a baking dish, layer meat sauce, three lasagna noodles, one-third of ricotta mixture, and sprinkle mozzarella. Repeat layering, finishing with meat sauce and remaining mozzarella.

Preheat oven to 375°F (190°C). Cover lasagna with foil and bake for 25 minutes. Remove foil and bake for another 25 minutes until bubbly and golden brown.

Let the lasagna rest for 15 minutes before slicing for easier serving.