Preheat the oven to 375°F (190°C).

Cook the lasagna noodles according to package instructions until al dente. Drain and lay them flat on a sheet or towel so they don’t stick.

In a large skillet over medium heat, cook the ground beef with the chopped onion and minced garlic. Break the meat into small pieces and cook until browned and no pink remains. Drain off excess fat.

Stir in the marinara sauce and simmer for about 5 minutes so flavors meld. Taste and season with salt and pepper if needed.

In a medium bowl, combine the ricotta cheese, egg, Italian seasoning, and a pinch of salt and pepper. Mix until smooth.

Spread a thin layer of meat sauce across the bottom of a 9×13 baking dish to prevent sticking.

Place three lasagna noodles over the sauce. Spread half the ricotta mixture across the noodles, then sprinkle with about one-third of the mozzarella. Add another layer of meat sauce.

Repeat: three more noodles, the remaining ricotta, another third of the mozzarella, and more meat sauce. Top with the final three noodles, the remaining meat sauce, and the last of the mozzarella.

Sprinkle the grated Parmesan evenly over the top. Cover the dish tightly with foil.

Bake covered for 25 minutes. Remove the foil and bake an additional 15 minutes, until the cheese is melted and bubbly and the edges are hot.

If you like a golden top, broil for 1–2 minutes while watching closely.

Let the lasagna rest for 10 minutes before slicing — this helps the layers set and keeps portions neat.