Prepare Meat Sauce: In a large skillet over medium heat, warm a drizzle of olive oil. Add ground beef and Italian sausage, cooking until browned, about 8-10 minutes. Stir in diced onion and minced garlic, cooking until onion is translucent, roughly 5 minutes. Mix in crushed tomatoes, tomato paste, sugar, basil, salt, and black pepper. Allow sauce to simmer for 30 minutes until thickened.

Cook Noodles: Bring a large pot of salted water to a boil. Add lasagna noodles and cook according to package instructions until al dente, which usually takes 8-10 minutes. Drain noodles and set aside in a single layer on a clean kitchen towel.

Mix Ricotta Filling: In a medium mixing bowl, combine ricotta cheese, egg, 2 cups of shredded mozzarella, and half of the grated Parmesan cheese. Mix until smooth and creamy.

Layer Lasagna: Preheat oven to 375°F (190°C). In a greased 9x13 inch baking dish, start layering with meat sauce, followed by noodles, ricotta mixture, and mozzarella cheese. Repeat layers two more times, finishing with meat sauce topped with remaining mozzarella and Parmesan cheese.

Bake: Cover baking dish tightly with aluminum foil. Bake in the oven for 25 minutes. Remove foil and bake for an additional 25 minutes, or until top is bubbling and golden brown.

Rest and Serve: After baking, let lasagna sit for 10-15 minutes. Before serving, sprinkle with freshly chopped parsley.