Brown the sausage with the onion and garlic. Drain and rinse under hot water.
Cook the spinach in 1 cup of water until soft and wilted. Drain and squeeze out the water, then coarsely chop the spinach.
Mix the sausage, spinach, ricotta and Italian cheese together.
Fill each cooked shell with the mixture.
Spread a bit of sauce on the bottom of two 9×13 pans. Put the stuffed shells in the pans as you fill them.
Cover with the rest of the sauce.
To bake, cover the pan with foil and bake at 350 degrees for 45 minute to 1 hour.
To freeze, cover tightly with foil and label with directions, “Thaw in fridge. Bake at 350 degrees for 1 hour”