Preheat your oven to 375°F (190°C).

Cook lasagna noodles in a large pot of boiling salted water according to the package instructions. Drain and lay them flat on parchment paper to prevent sticking.

Heat olive oil in a skillet over medium heat. Add the chopped onion and minced garlic, sautéing until the onion is translucent.

Add ground beef to the skillet and cook until browned. Drain any excess fat.

Stir in marinara sauce and let it simmer for about 10 minutes, seasoning with salt and pepper to taste.

In a bowl, whisk the egg into the ricotta cheese until combined.

Assemble your lasagna: Spread a thin layer of meat sauce on the bottom of a baking dish. Layer with noodles, the ricotta mixture, and a sprinkle of mozzarella cheese. Repeat the layers until all ingredients are used, finishing with noodles and sauce on top.

Sprinkle remaining mozzarella and Parmesan on top, cover with foil, and bake for 25 minutes.

Remove the foil and bake for another 15 minutes until the cheese is bubbly and golden.

Let it rest for 10 minutes before serving to allow the layers to set.