Prepare the meat sauce:
In a large skillet, heat a tablespoon of olive oil over medium heat. Add the ground beef and sausage, breaking it up with a spoon. Cook until browned.
Add the chopped onion and minced garlic, cooking for another 2-3 minutes until softened.
Stir in the crushed tomatoes, tomato paste, and tomato sauce. Add oregano, basil, crushed red pepper flakes, salt, pepper, and sugar.
Bring the sauce to a simmer, then reduce the heat and let it cook for 30-40 minutes, stirring occasionally. The sauce should thicken and the flavors will meld together.
Prepare the cheese mixture:
In a large mixing bowl, combine ricotta cheese, 2 cups of mozzarella, Parmesan, egg, nutmeg, salt, and pepper. Stir until smooth and well combined.
Cook the lasagna noodles:
Bring a large pot of salted water to a boil. Cook the lasagna noodles according to package instructions (usually 8-10 minutes). Drain and set aside. If using no-boil noodles, simply skip this step.
Assemble the lasagna:
Preheat the oven to 375°F (190°C). Lightly grease a 9x13-inch baking dish with olive oil.
Start with a layer of meat sauce on the bottom of the dish, followed by a layer of noodles. Then, spread a layer of the cheese mixture over the noodles.
Repeat the layering process until you run out of ingredients, finishing with a generous layer of sauce and a sprinkle of mozzarella cheese on top.
Bake the lasagna:
Cover the lasagna with aluminum foil and bake for 25 minutes. Then, remove the foil and bake for an additional 20 minutes, or until the cheese is bubbly and golden brown.
Let it rest:
Allow the lasagna to rest for 10-15 minutes before slicing. This will help the layers set and make it easier to serve.
Serve:
Garnish with fresh parsley, slice, and serve hot! Pair with garlic bread and a salad for a complete meal.