Preheat the oven to 400 degrees F and position the oven rack in the middle.
To make the meat sauce, heat the olive oil in a large saucepan. Add the onion and cook over medium-low heat until translucent (about 5 minutes). Add the garlic and stir for one more minute. Then add the sausage and cook over medium-low heat. Breaking it up with a wooden spoon, for 10 to 15 minutes, or until fully cooked and no longer pink. Add the crushed tomatoes, tomato sauce, tomato paste, oregano, basil, sea salt, and freshly ground black pepper. Simmer uncovered over medium-low heat for 20 minutes.
Soak lasagna noodles in hot tap water.
While the sauce is simmering, make the cheese filling In a large bowl, combine the ricotta, 1 cup of Parmesan, the beaten egg, chopped parsley, sea salt, and freshly ground black pepper. Set aside.
Ladle one third of the meat sauce into a 9”x 12”x 2” casserole or baking pan. Spread the sauce over the bottom of the dish. Then add approximately half the pasta (in one layer, cover the sauce with the noodles), half the sliced mozzarella, half the cheese mixture, and one third of the sauce. Add another single layer of noodles, mozzarella, ricotta, and the remaining sauce Sprinkle with the remaining ½ cup of Parmesan.
Bake uncovered for 35 minutes, or until the sauce is bubbling.