Pasta Shells with Sausage, Spinach and Cheese

I came across this recipe in a Redbook magazine, and thought it would be a great crowd-pleaser.  Think of it as lasagna stuffed in shell pasta, rather than layered in a casserole.  One batch will fill two 9x13 casserole pans, enough to feed four to six people.

Ingredients:
12 oz package jumbo pasta shells
2 tbsp olive oil
1/2 cup onion, chopped
1 lb ground Italian sausage
2 cloves garlic, minced
1 large egg
16 oz tub ricotta or cottage cheese
9 oz frozen spinach, thawed
1/2 cup grated Parmesan cheese
6 oz shredded cheese (Mozzarella or Cheddar Jack)
32 oz tomato sauce

Directions:
1. Bring a large pot of water to boil, add pasta shells and cook according to package directions.  Drain in a colander, rinse under cold water and set aside to dry.
2. While pasta water is boiling, heat oil in a large skillet and add onion, cook until softened.  Add sausage, breaking up into small bits, and cook until no longer pink.  Add garlic and cook for another minute.  Remove pan from heat.
3.  Combine egg and ricotta cheese in a large bowl.  Add spinach, Parmesan cheese, 4 oz of the shredded cheese, and the cooled sausage mixture.  Stir it all until well combined.
4.  Preheat oven to 350 degrees.  Spread a few spoonfuls of tomato sauce along the bottom of the pans until the bottom is covered.  Fill pasta shells with the cheese and sausage mixture, then arrange them in rows in the pans.  Spread the remaining tomato sauce over the top of the shells.  Cover the pans with foil and bake for 30 minutes.  Remove the foil, sprinkle with remaining shredded cheese, and bake for another 10 minutes.