Bring a large pot of salted water to a boil. This helps to flavor the pasta as it cooks.

Add the spaghetti and cook according to package instructions until al dente, usually about 8-10 minutes.

Once cooked, drain the spaghetti in a colander and set aside.

In a skillet over medium heat, add the ground beef. Cook until browned, breaking it apart with a wooden spoon, about 5-7 minutes.

Add the chopped onion and minced garlic to the skillet. Sauté until the onion is translucent, about 3-4 minutes.

Stir in the crushed tomatoes, tomato paste, oregano, basil, salt, and pepper. Bring the mixture to a simmer and let it cook for 10 minutes, allowing the flavors to meld.

In a mixing bowl, combine the ricotta cheese, 1 cup of mozzarella cheese, ½ cup of Parmesan cheese, and the beaten egg. Mix until well combined. This will create a creamy layer in the baked spaghetti.

Preheat your oven to 350°F (175°C).

In a large baking dish, layer half of the cooked spaghetti on the bottom.

Spread half of the meat sauce over the spaghetti, followed by half of the cheese mixture. Repeat the layers with the remaining spaghetti, meat sauce, and cheese mixture.

Top the assembled dish with the remaining ½ cup of mozzarella cheese and ¼ cup of Parmesan cheese for a golden, bubbly topping.

Cover the baking dish with aluminum foil and bake in the preheated oven for 20 minutes.

Remove the foil and bake for an additional 10 minutes, or until the cheese is melted and bubbly.

Let the baked spaghetti cool for 5 minutes before serving. This helps the layers set and makes serving easier.