Heat the oven: Heat the oven to 375 F and bring a large pot of salted water to a boil for the noodles.

Start the sauce: Warm the olive oil in a Dutch oven over medium-high heat, add the beef and onion, and cook until the meat is browned and the onion is soft. Spoon off any excess fat into a heat-safe bowl if the pot looks greasy.

Add the aromatics: Stir in the garlic and tomato paste and cook for 1 minute.

Simmer the meat sauce: Add the crushed tomatoes, oregano, 1 1/2 teaspoons of the salt, and the black pepper and simmer the sauce for 15 minutes until thickened. While the sauce simmers, add the lasagna noodles to the boiling water and cook them 2 minutes less than the package directions.

Drain the noodles: Drain the noodles and lay them on a lightly oiled sheet pan so they do not stick together.

Mix the ricotta filling: Stir the ricotta with the egg, 1/2 cup of the Parmesan, half of the parsley, and the remaining 1/2 teaspoon salt.

Build the first layer: Spread about 3/4 cup of meat sauce in a 9-by-13-inch baking dish, top with 3 noodles, then add half of the ricotta mixture, about one-third of the mozzarella, and about 1 cup more sauce.

Build the second layer: Top with 3 more noodles, the remaining ricotta mixture, about one-third of the mozzarella, and about 1 1/4 cups more sauce.

Build the top layer: Top with the last 3 noodles, spread over the remaining sauce, and scatter on the remaining mozzarella and Parmesan.

Bake covered: Cover the dish tightly with lightly oiled foil and bake for 20 minutes so the center heats through without drying the top.

Brown the top: Uncover the lasagna and bake for 8 to 10 minutes more, until the top is browned in spots and the edges are bubbling.

Rest and serve: Let the lasagna rest for 10 minutes, then sprinkle with the remaining parsley and cut into slices.