Preheat your oven to 375°F.
In a large skillet, cook the chopped onion over medium heat for 3–4 minutes until softened.
Add the minced garlic and cook for another 1 minute until fragrant. Add the ground beef to the skillet and cook for 5–7 minutes, breaking it up as it cooks, until browned. Drain any excess fat.
Stir in the marinara sauce, oregano, basil, salt, and pepper. Let it simmer for 5–7 minutes, then remove from heat.
In a separate bowl, combine the ricotta cheese, mozzarella cheese (reserve 1 cup for topping), Parmesan cheese, and egg. Mix until smooth and well combined.
In a large Dutch oven, start with a layer of the beef marinara sauce on the bottom. Follow with a layer of uncooked lasagna noodles (you may need to break the noodles to fit).
Spread a layer of the ricotta cheese mixture over the noodles, followed by another layer of beef marinara sauce. Repeat layering in this order until all ingredients are used, ending with a layer of marinara sauce on top.
Sprinkle the reserved mozzarella cheese over the top layer of marinara sauce.
Cover the Dutch oven with a lid and bake in the oven for 45 minutes.
Remove the lid and bake for another 15–20 minutes until the cheese is bubbly and golden.
Let the lasagna rest for 10 minutes before slicing and serving.