Preheat oven to 375°F (190°C). In a large pot or Dutch oven, brown ground beef over medium-high heat. Drain any excess fat.
Add chopped onions and garlic to the pot and cook until softened, about 5 minutes.
Stir in tomato paste, crushed tomatoes, tomato sauce, Italian seasoning, sugar, salt, and pepper. Bring to a simmer, then reduce heat and cook for 30 minutes, stirring occasionally.
In a separate bowl, combine ricotta cheese, egg, Parmesan cheese, and parsley. Mix well.
Spread a thin layer of meat sauce in the bottom of a 9x13 inch baking dish. Arrange a layer of lasagna noodles over the sauce, overlapping as needed.
Spread half of the ricotta mixture over the noodles, followed by a layer of mozzarella cheese and another layer of meat sauce.
Repeat layers: noodles, remaining ricotta mixture, mozzarella cheese, and meat sauce. Top with a final layer of noodles, remaining meat sauce, and a generous layer of mozzarella and Parmesan cheese.
Cover the baking dish with aluminum foil and bake for 25 minutes. Remove the foil and bake for an additional 20 minutes, or until the cheese is melted and bubbly and the lasagna is heated through.
Let the lasagna rest for 10-15 minutes before slicing and serving.
