Preheat your oven to 400°F (200°C).

In a large pot, bring salted water to a boil. Add the manicotti shells and cook for about 5 minutes until slightly al dente. Drain and rinse with cold water.

In a mixing bowl, stir the marinara sauce with heavy cream if using. Pour a layer into the bottom of the casserole dish.

In a large bowl, combine eggs, ricotta, half of the mozzarella, half of the parmesan, garlic, parsley, salt, pepper, and nutmeg. Mix until cohesive.

Fill each manicotti shell with the cheese filling using a piping bag. Arrange them in the casserole dish over the marinara sauce.

Cover the filled manicotti with the remaining sauce and sprinkle with the rest of the mozzarella and parmesan.

Cover the dish with foil and bake for 25 minutes. Remove foil and bake for an additional 10 minutes until bubbly.

Let the manicotti rest for 5 minutes before serving. Garnish with extra parsley.