Preheat oven to 375°F (190°C). Lightly grease a 9x13 inch baking dish.
Heat olive oil in a large skillet over medium-high heat. Add ground meat and onion; cook, breaking up the meat with a spoon, until meat is browned and onion is softened, about 7-10 minutes. Drain off any excess grease.
Add minced garlic to the skillet and cook for 1 minute more, until fragrant. Stir in tomato paste, oregano, basil, Italian seasoning, sugar, salt, and pepper. Cook for another minute, stirring constantly, to toast the spices and deepen the flavor.
Pour in crushed tomatoes. Bring to a simmer, then reduce heat to low and let simmer, uncovered, for at least 15 minutes, or up to 30 minutes, stirring occasionally. The longer it simmers, the richer the flavor will be! Taste and adjust salt and pepper as needed.
In a medium bowl, combine ricotta cheese, ½ cup Parmesan cheese, egg, salt, and pepper. Mix well until smooth and creamy.
Spread a thin layer of meat sauce in the bottom of the prepared baking dish. Top with a layer of lasagna noodles (you may need to break some to fit). Spread about half of the ricotta mixture over the noodles, then sprinkle with ⅓ of the mozzarella cheese.
Layer with more noodles, remaining ricotta mixture, another ⅓ of the mozzarella, and then another layer of noodles. Top with the remaining meat sauce and the remaining mozzarella and Parmesan cheese.
Cover the baking dish tightly with aluminum foil. Bake for 30 minutes. Remove foil and bake for another 15-20 minutes, or until the lasagna is bubbly and the cheese is melted and lightly golden brown. Let stand for 10-15 minutes before cutting and serving. This resting time is crucial for the lasagna to set and slice neatly!
Sprinkle with fresh parsley, if desired. Serve hot and enjoy!