Preheat the oven to 375°F. Cook the lasagna noodles in a large pot of boiling water until al dente, then drain and set aside.

Brown the Italian sausage in a skillet over medium heat, breaking it into small pieces as it cooks. Drain any excess fat and set the sausage aside.

Stir together the ricotta cheese, egg, Italian seasoning, and salt in a mixing bowl until well combined.

Spread 1 cup of marinara sauce across the bottom of a 9x9 baking dish. Arrange 4 noodles on top of the sauce.

Spread half the ricotta mixture over the noodles, followed by half the cooked sausage, 1/2 cup marinara sauce, and 3/4 cup mozzarella.

Repeat the layers with the remaining noodles, ricotta mixture, sausage, 1/2 cup marinara sauce, and 3/4 cup mozzarella.

Top the final layer with the remaining 1 cup marinara sauce, 1/2 cup mozzarella, and all of the Parmesan cheese.

Cover the dish with foil and bake for 25 minutes. Remove the foil and bake 10 minutes more until the cheese is melted and lightly browned. Let the lasagna rest 10 minutes before slicing.