Preheat oven to 350°F (175°C).

Boil the large box of shells until al dente, then drain thoroughly.

In a large bowl, combine the 3 cups of shredded Mozzarella cheese (reserve 1 cup for topping), 8 oz of small curd cottage cheese, 1 can of drained spinach (optional), 1 egg, and 8 oz of Ricotta cheese.

Mix the filling ingredients well until thoroughly combined.

Pour half of the spaghetti sauce into the bottom of a large baking pan.

Using a large tablespoon, spoon the cheese filling into each shell.

Place the stuffed shells in the baking pan on top of the sauce.

Cover the shells with the remaining spaghetti sauce.

Sprinkle the remaining 1 cup of Mozzarella cheese over the top.

Cover the baking pan tightly with foil.

Bake in the preheated oven for 1 hour.

Remove the foil and bake for additional 5 minutes to brown cheese.

Let cool for a few minutes before serving.

Enjoy!