01 - Preheat oven to 375°F (190°C).
02 - Heat olive oil in a large skillet over medium heat. Add onion and cook until softened, about 5 minutes. Stir in garlic and cook for 1 minute more.
03 - Add ground beef, salt, black pepper, oregano, basil, and red pepper flakes. Cook, breaking up the meat with a spoon, until browned, approximately 6 minutes.
04 - Stir in crushed tomatoes, tomato paste, and sugar. Simmer uncovered for 15 to 20 minutes, stirring occasionally, until the sauce thickens. Adjust seasoning as desired.
05 - If not using no-boil noodles, cook lasagna noodles according to package instructions. Drain and lay flat on a towel to prevent sticking.
06 - Combine ricotta cheese, egg, Parmesan, parsley, salt, and pepper in a mixing bowl. Stir until smooth and evenly blended.
07 - Spread 1 cup of meat sauce in the bottom of a 23x33 cm (9x13 inch) baking dish. Layer 4 noodles evenly over the sauce.
08 - Spread one-third of ricotta mixture on noodles, top with 1 cup meat sauce, and then 1 cup shredded mozzarella. Repeat the layering two more times, ending with remaining meat sauce and mozzarella. Sprinkle with reserved Parmesan cheese.
09 - Cover dish with foil, lightly oiled or lined with parchment to prevent sticking. Bake for 25 minutes.
10 - Remove foil and continue baking for an additional 20 to 25 minutes, until cheese is bubbly and golden brown.
11 - Allow lasagna to rest for 15 minutes before slicing to ensure clean portions.