• Fill a large pot with water and add a pinch of salt. Place the pot on the stove and bring the water to a boil. Once boiling, add the pasta shells and cook them according to the directions on the package.When the shells are cooked, drain them in a colander.
• While the water is boiling, preheat your oven to 350 degrees Fahrenheit. Spread 1/2 cup of spaghetti sauce on the bottom of a 9×9 inch baking dish. Set the dish aside for later.
• Heat a medium skillet over medium heat. Add the uncooked sausage to the skillet. Cook the sausage, breaking it into small pieces with a spatula, until it is browned and fully cooked (about 3 to 5 minutes).
• Remove the skillet from the heat.Stir in 1 cup of spaghetti sauce with the sausage.

Filling:

• In a large bowl, combine the cooked sausage mixture, ricotta cheese, 1/2 cup of shredded mozzarella cheese, Parmesan cheese, egg, and spinach. Stir everything together until well mixed.

Assembly

• Take a cooked pasta shell and spoon about 1-2 tablespoons of the filling mixture into it. Place the filled shell into the sauce-lined baking dish. Repeat this process until all the shells are filled and the dish is full. It’s okay if the shells are close together.
• Spread the remaining 1/2 cup of spaghetti sauce over the stuffed shells. Sprinkle the remaining shredded mozzarella cheese generously on top.
• Cover the baking dish with aluminum foil.Place the dish in the preheated oven and bake for 20 minutes.After 20 minutes, remove the foil and bake for an additional 10 minutes, or until the cheese is melted and bubbly.

Freeze Instructions:

• Follow the instructions above until just before baking. Cover securely with heavy duty foil or a freezer container.
• Take your stuffed shells out of the freezer the day before you plan on cooking them. Let them slightly thaw in the refrigerator.
• Bake at 350 degrees, covered, for 45 minutes. Remove the foil and bake an additional 20 minutes.