While the sauce is simmering, take a medium bowl and combine the ricotta cheese, the egg, half of the parmesan cheese, and the fresh parsley. Use a fork or a whisk to mix everything together until it is smooth and well combined. This mixture will act as the creamy layer that balances the acidity of the tomato sauce. Keep this mixture in the refrigerator until you are ready to assemble the lasagna.
Bring a large pot of salted water to a boil and cook the lasagna noodles according to the package directions, usually for about 8 to 10 minutes. Aim for al dente, as the noodles will continue to cook in the oven. Once they are done, drain them and lay them out flat on a sheet of parchment paper or a clean towel so they do not stick to each other. If you are using no boil noodles, you can skip this step entirely.
Preheat your oven to 375 degrees Fahrenheit. Spread about one cup of the meat sauce onto the bottom of a large baking dish. Place a single layer of noodles over the sauce, followed by a third of the ricotta mixture and a generous sprinkle of mozzarella cheese. Repeat these layers, sauce, noodles, ricotta, and mozzarella, until you reach the top of the dish. For the final layer, finish with a thick coating of meat sauce, the remaining mozzarella, and the rest of the parmesan cheese.
Cover the baking dish tightly with aluminum foil, making sure it does not touch the cheese to prevent sticking. Bake in the oven for 25 minutes, then remove the foil and bake for another 20 to 25 minutes until the cheese is golden brown and bubbling. Once finished, remove the lasagna from the oven and let it rest for at least 15 minutes before slicing. This resting period is crucial because it allows the layers to set, making it much easier to serve clean squares.
