Preheat the oven to 350 degrees.
Cook the lasagna noodles according to the package directions, until al dente. Drain and arrange in a single layer on a large piece of aluminum foil or parchment paper. Note: If using oven-ready (no-boil) or fresh lasagna noodles, you may skip this step.
Meanwhile, brown the beef and sausage together in a large skillet over medium-high heat, breaking up the meat as it cooks. If necessary, drain away any fat.
Add the onion, garlic, and Italian seasoning and cook for 3 minutes, until the onion is soft and the herbs are fragrant.
Add the marinara sauce and tomato paste and bring to a simmer. Reduce the heat to medium-low and simmer, uncovered, for 5 to 7 minutes, until slightly thickened. Season to taste with salt and black pepper.
To make the cheese layer, in a medium bowl, combine the ricotta cheese, 2 cups of the mozzarella cheese, 1/2 cup of the parmesan cheese, fresh parsley, and egg. Mix well.
Spoon a heaping cup of the meat sauce into the bottom of a 13x9-inch baking dish. Spread out to cover the bottom of the pan.
Arrange 3 lasagna noodles over the sauce. It’s fine if the noodles are slightly overlapping.
Top the noodles with 1/3 of the ricotta mixture.
Top with 1 cup of the meat sauce.
Repeat two more times (3 noodles-1/3 of the ricotta-1 cup sauce).
Top with the remaining 3 noodles and remaining sauce.
Top with the remaining 2 1/2 cups of mozzarella cheese and 1/4 cup of parmesan cheese.
Cover the pan with aluminum foil and bake for 45 minutes. If desired, coat the foil with cooking spray to prevent the cheese from sticking.
Remove the aluminum foil and bake for 15 more minutes, until the cheese is bubbly. If desired, place the pan under the broiler to brown the cheese.
Let the lasagna rest for at least 15 minutes before cutting and serving.