Preheat the oven to 365 degrees F (185 degrees C).
Bring a large pot of salted water to a boil; cook lasagna noodles until tender with a bite, 8 to 10 minutes; drain.
Set a skillet over medium heat, add Italian sausage, and cook, breaking up clumps with a spatula, until browned and crumbly, about 5 minutes. Remove from skillet and drain on paper towels.
Scoop ricotta into a bowl and crack in the egg. Sprinkle with 1 tablespoon Parmesan cheese and 1/2 cup mozzarella. Stir to combine; set aside.
Pour a bit of marinara on the bottom of a deep casserole dish, and spread to cover. Lay 3 noodles side-by-side over sauce.
Spread a little more sauce over noodles; then dollop 1/3 of ricotta mixture over the sauce, spreading as evenly as possible. Sprinkle 1/3 of remaining mozzarella and 1/3 of Parmesan cheese on top of ricotta. Sprinkle with 1/3 of sausage. Layer 1/3 pepperoni slices on top.
Repeat layers 2 more times with remaining ingredients. Cover the dish tightly with foil.
Bake in the preheated oven for 30 minutes. Remove foil; bake until nicely browned, about 10 minutes. Let stand 5 minutes before cutting.
