Preheat oven to 375°F (190°C).
Bring a large pot of salted water to a boil. Cook lasagna noodles for 8-10 minutes until al dente. Drain and lay flat on parchment paper to prevent sticking.
In a large skillet over medium-high heat, brown the ground beef and Italian sausage until fully cooked. Drain excess grease.
Add onion and garlic to the skillet. Cook for 5 minutes until soft.
Stir in crushed tomatoes, tomato paste, oregano, salt, and pepper. Simmer on low heat for 20 minutes.
In a separate bowl, mix ricotta cheese, egg, and parsley until well combined.
Spread 1 cup of meat sauce onto the bottom of a 9x13 inch baking dish.
Place 3 or 4 noodles over the sauce. Spread 1/3 of the ricotta mixture over the noodles, then top with 1 cup of meat sauce and 1 1/4 cups of mozzarella cheese.
Repeat the layers (noodles, ricotta, sauce, mozzarella) twice more.
Top the final layer of noodles with the remaining meat sauce, mozzarella, and Parmesan cheese.
Cover the dish tightly with foil and bake for 25 minutes.
Remove the foil and bake for an additional 25 minutes until the cheese is bubbling and golden.
Let the lasagna rest for 15 minutes to allow the structure to set before slicing.