01 - Set the oven to 375°F (190°C) to prepare for baking.
02 - Heat olive oil in a large skillet over medium heat. Add the chopped onion and sauté until softened, about 5 minutes. Stir in minced garlic and cook for an additional minute.
03 - Add ground beef along with salt, black pepper, oregano, basil, and optional crushed red pepper flakes. Cook until browned, breaking the meat apart, approximately 6 minutes.
04 - Incorporate crushed tomatoes, tomato paste, and sugar. Let the sauce simmer uncovered for 15 to 20 minutes, stirring occasionally, until thickened. Adjust seasonings as needed.
05 - While the sauce simmers, boil noodles according to package instructions unless using no-boil variety. Drain and lay flat on a towel to prevent sticking.
06 - Combine ricotta cheese, egg, grated Parmesan, parsley, salt, and black pepper in a bowl. Mix thoroughly until smooth.
07 - Spread 1 cup of meat sauce in the bottom of a 9x13 inch baking dish. Arrange 4 noodles atop the sauce. Spread one-third of the ricotta mixture over noodles, followed by 1 cup of meat sauce and 1 cup mozzarella. Repeat two more times, ending with remaining meat sauce and mozzarella. Sprinkle remaining Parmesan on top.
08 - Cover the dish with foil (lightly greased or lined with parchment to prevent sticking). Bake in the preheated oven for 25 minutes.
09 - Remove the foil and bake an additional 20 to 25 minutes until the top is bubbly and golden brown.
10 - Allow lasagna to rest for 15 minutes to set before slicing and serving.