Cook and drain spinach: Preheat the oven to 375°F. Bring a large pot of water to a boil, and set up a large colander in the sink. Drop the spinach into the boiling water, stirring with each addition. Bring the water back to a boil for a few seconds, just until the spinach is bright green, then drain the spinach, and rinse with cold water. Drain the spinach and wring it out by the handful, then spread the spinach on a kitchen towel. Wrap the towel around the spinach and roll it up, and press down to press all the water out of the spinach. Set aside until ready to use.

Cook pasta: Bring a large pot of water to a boil, and stir in 1 Tbsp. salt. Cook the pasta shells for a minute less than the package directs, about 9 minutes, then drain.

Make filling: In a large bowl, combine the prepared spinach, ricotta cheese, egg, parsley, salt, pepper and a cup of the shredded Parmesan cheese. Stir to mix well. In a medium bowl mix together the remaining half cup of Parmesan cheese and the mozzarella. Set aside.

Assemble dish: Pour the marinara sauce in a broiler-safe 9- x 13-inch baking pan and spread into an even layer. Use a teaspoon to form rounded portions of spinach filling, then gently stuff each into a cooked shell. Place in the baking pan as you go.

Add cheese: When all the shells are filled, top with the mozzarella mixture. Cover the pan with foil, crimping it tightly around the rims.

Bake, then broil: Bake in preheated oven 30 minutes. Uncover the pan and turn on the broiler. Place the pan under the broiler and watch carefully as it quickly browns the cheese. Let stand 5 minutes before serving.