Start by boiling the lasagna noodles in salted water until they are just al dente. I always make sure not to overcook them because they continue cooking in the oven. Once done, drain and lay them flat to prevent sticking.
In a skillet, cook the ground beef and Italian sausage until browned and fully cooked. Add chopped onions and garlic, letting them soften and release their aroma. Stir in the marinara sauce and let it simmer so all the flavors blend beautifully.
In a bowl, mix ricotta cheese with egg, parsley, salt, and pepper until smooth. This mixture should be creamy and well combined. I like to taste it slightly to adjust seasoning before layering.
Spread a thin layer of meat sauce at the bottom of your baking dish. Add a layer of noodles, followed by ricotta mixture, mozzarella, and more sauce. Repeat the layers until everything is used, finishing with cheese on top.
Cover the dish with foil and bake in a preheated oven at 375°F (190°C). After about 30 minutes, remove the foil and bake for another 15 minutes until the top is bubbly and golden. Let it rest before slicing to keep the layers intact.