01 - Set oven temperature to 375°F.
02 - Heat olive oil in a large skillet over medium heat. Sauté chopped 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; brown meat while breaking it up. Drain excess fat if necessary. Mix in tomato paste and cook for 1 minute. Add crushed tomatoes, tomato sauce, and sugar, then simmer uncovered for 20–25 minutes until thickened, stirring occasionally. Remove from heat.
03 - Combine ricotta cheese, egg, Parmesan, parsley, salt, and pepper in a medium bowl. Blend until smooth.
04 - Cook lasagna noodles according to package directions if using regular noodles. Drain and set aside. Omit this step with no-boil noodles.
05 - Spread 1 cup meat sauce on the bottom of a 9x13 inch baking dish. Layer 4 noodles over the sauce, spread one-third of the ricotta mixture, 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 with remaining mozzarella and Parmesan cheese.
06 - Cover dish with foil (lightly oil foil underside to prevent sticking). Bake for 25 minutes at 375°F.
07 - Remove foil and continue baking for 20–25 minutes until cheese is golden and bubbly.
08 - Allow the dish to rest for 15 minutes before slicing to set layers.