01 - Set oven temperature to 375°F.
02 - Heat olive oil in a large skillet over medium heat. Sauté onion until softened, about 3–4 minutes. Add garlic and cook for 1 minute. Incorporate ground beef, salt, pepper, oregano, basil, and red pepper flakes; cook, breaking up meat, until browned. Drain fat if necessary. Stir in tomato paste and cook 1 minute. Add crushed tomatoes, tomato sauce, and sugar. Simmer uncovered for 20–25 minutes until thickened, stirring occasionally. Remove from heat.
03 - Combine ricotta, egg, grated Parmesan, parsley, salt, and pepper in a medium bowl. Stir until smooth.
04 - Cook lasagna noodles according to package instructions if not using no-boil noodles. Drain and set aside.
05 - Spread 1 cup meat sauce evenly in the bottom of a 9x13-inch baking dish. Layer 4 noodles over the sauce. Spread one-third of the ricotta mixture over noodles and sprinkle with 1 cup mozzarella. Top with approximately 1 1/2 cups meat sauce. Repeat layering two more times, finishing with noodles and remaining meat sauce. Sprinkle top evenly with remaining mozzarella and Parmesan cheeses.
06 - Cover the dish tightly with aluminum foil sprayed with oil on the underside to prevent sticking. Bake for 25 minutes.
07 - Remove foil and bake an additional 20–25 minutes until cheese is golden and bubbling.
08 - Allow to rest for 15 minutes before slicing to set and serve.