Preheat the oven to 375 degrees and bring a large pot of salted water to a boil. Cook the lasagna noodles until al dente, then drain and set aside.

In a large skillet over medium heat, cook the Italian sausage until browned and no longer pink. Drain any excess fat and stir in 1 1/2 cups of the marinara sauce. Remove from heat.

In a mixing bowl, combine the ricotta cheese, egg, Italian seasoning, salt, and black pepper. Stir until smooth.

Spread a thin layer of the remaining marinara sauce in the bottom of an 8x8 baking dish. Lay 4 noodles across the sauce.

Spread half the ricotta mixture over the noodles, followed by half the sausage sauce and 1 cup of mozzarella. Repeat the layers once more, ending with the remaining mozzarella and all of the Parmesan on top.

Cover the dish with foil and bake for 25 minutes. Remove the foil and bake 10 minutes longer until the cheese is bubbly and lightly golden. Let the lasagna rest 10 minutes before slicing.