Cook the ground beef and Italian sausage in a large pot over medium-high heat for 8 minutes, drain excess fat, add onion and cook 4 to 5 minutes, then add garlic and cook 1 minute more. Stir in the tomato paste, crushed tomatoes, oregano, basil, sugar, salt, pepper, and red pepper flakes, then simmer uncovered on low for 30 minutes until thickened.

Boil the lasagna noodles in salted water with 1 tbsp olive oil, cooking 2 minutes less than the package directions. Drain and lay flat on an oiled baking sheet.

Stir together the ricotta, eggs, parsley, and nutmeg in a large bowl until smooth.

Heat the oven to 375°F (190°C). Spread 1 cup of meat sauce in a 9x13-inch baking dish, then layer noodles, ricotta, meat sauce, and mozzarella three times. Top with the final 4 noodles, remaining meat sauce, remaining mozzarella, and all of the Parmesan.

Cover tightly with foil and bake for 30 minutes, then remove the foil and bake another 20 to 25 minutes until the cheese is bubbling and golden. Rest for 15 minutes before cutting.

Slice into 8 portions, plate with layers visible, and top with extra parsley and Parmesan before serving.