2. Heat a large nonstick skillet over high heat. Wash the spinach and add it to the skillet with just the water that clings to the spinach leaves. Toss the spinach until it is wilted and remove from heat.
3. Transfer the spinach to a food processor and puree. Add the ricotta cheese, egg and Parmesan cheese and puree again. Transfer the spinach mixture to a mixing bowl, add the bread crumbs and generously season with salt, pepper and nutmeg.
4. Using a spoon, fill the manicotti with the spinach mixture.
5. Preheat the oven to 350°F.
6. Spread 1/2 cup of tomato sauce on the bottom of a large baking dish. Add the filled manicotti in a single layer and cover with the remaining tomato sauce. Cover the entire dish with foil.
7. Bake for 20 minutes. Remove the foil and continue to bake until the edges of the dish are bubbly, about 10 more minutes.