In a large pot, bring salted water to a boil. Add the spaghetti and cook according to the package instructions until al dente. Reserve about a cup of pasta water, then drain the rest and set aside.

In a large skillet over medium heat, cook the ground sausage until browned. Stir in your marinara sauce and let it simmer for about 10 minutes. If the sauce seems too thick, add a splash of the reserved pasta water until desired consistency is reached.

In a bowl, combine ricotta cheese, half of the mozzarella, half of the Parmesan, Italian seasoning, salt, and pepper. Mix until well-combined, creating a creamy filling.

Preheat your oven to 350°F (175°C). In a baking dish, spread a thin layer of the meat sauce on the bottom. Layer half of the spaghetti, followed by the ricotta mixture. Pour over half of the remaining meat sauce, then repeat the layering process.

Finish with a layer of the remaining mozzarella and Parmesan cheese on top, covering every inch for a cheesy, bubbling surface.

Cover with foil and bake for 25 minutes. Remove the foil and bake for an additional 15 minutes or until golden and bubbling.

Let it cool for a few minutes, slice, and serve hot.