Preheat oven to 375°F (190°C). Brown the lean ground beef in a large skillet. Drain any excess fat. Add the chopped onion and minced garlic, cooking until softened.

Stir in the marinara sauce, tomato sauce, dried oregano, dried basil, and red pepper flakes (if using). Bring to a simmer and cook for 10 minutes to allow flavors to meld.

In a separate bowl, combine the ricotta cheese, cottage cheese, grated Parmesan cheese, and large egg. Mix well until thoroughly combined.

Cook the lasagna noodles according to package directions. Drain and rinse them with cold water to prevent sticking.

To assemble, spread a thin layer of meat sauce on the bottom of a 9x13 inch baking dish. Arrange a layer of cooked lasagna noodles over the sauce. Spread half of the ricotta mixture over the noodles, then top with a layer of meat sauce and a sprinkle of mozzarella cheese. Repeat the layers, ending with a layer of mozzarella cheese on top.

Cover the baking dish with aluminum foil and bake for 30 minutes. Remove the foil and bake for an additional 15-20 minutes, or until the cheese is melted and bubbly and the edges are lightly browned.

Let the lasagna stand for 10-15 minutes before slicing and serving. This allows the layers to set, making it easier to cut neatly.