Cook the lasagna noodles in a large pot of salted boiling water until al dente. Drain and set aside.
In a large skillet over medium heat, cook the ground beef and Italian sausage until browned. Drain excess fat.
Add chopped onion and minced garlic to the meat mixture, cooking until the onion is translucent.
Stir in marinara sauce and bring to a simmer for about 10 minutes. Add salt, pepper, oregano, and basil to taste.
In a separate bowl, mix the ricotta cheese, egg, salt, and pepper until well combined.
In a 9x13 inch baking dish, spread a thin layer of the meat sauce at the bottom. Layer 4 lasagna noodles on top.
Spread half of the ricotta mixture over the noodles, then sprinkle with one-third of the mozzarella cheese.
Repeat the layers: add another layer of meat sauce, 4 more noodles, the remaining ricotta mixture, and another third of mozzarella.
Top with the last 4 noodles, the remaining meat sauce, and finish with the rest of the mozzarella and all the Parmesan cheese.
Cover the dish with aluminum foil and bake for 25 minutes. Remove the foil and bake for an additional 15-20 minutes, until the cheese is bubbly and slightly golden.
Let the lasagna cool for 10 minutes before slicing. Garnish with fresh basil leaves before serving.
Notes
Let the lasagna cool before slicing for cleaner pieces.