Preheat oven to 350℉
Slip each sausage out of its casing, add a little water to your skillet and cook for about 8-10 minutes. Crumble up the sausage with a spatula while it sautés. Spoon into a bowl and set aside.
Season ground beef with salt. Brown the beef in a pan, drain off about half the fat, and then add one cup of sauce, stir occasionally and let the meat sauce simmer for a minute or two.
Mix ricotta cheese, egg, parsley, salt and pepper in a bowl. Set aside.
Spoon some sauce on the bottom of your baking dish. Layer with pre cooked lasagna sheets, ground beef mixture, half of the mozzarella cheese, then another layer of lasagna sheets, ricotta cheese mixture, sausage, lasagna sheets, some tomato sauce, and the rest of the mozzarella cheese and then the final layer of lasagna sheets, tomato sauce and parmesan cheese.
Cover and bake for 45 minutes. Then remove the cover and bake for 10 minutes more. Let stand for 10 minutes before cutting.