Stuffed Shells (sausage, spinach, and cheese)

This is from Redbook magazine and really tasty. Now, they say prep is 15 minutes but I disagree. It took me that long to just stuff the shells - though it wasn't horribly time consuming... I just wouldn't make it on a weeknight. The pan in the pic is 9x13 - I had enough shells to fill that entire pan plus an 8x8 pan. However, I think I used more sausage than it called for... I just used the whole package, which was about a pound.

Sausage, spinach, and cheese stuffed shells
1 12-ounce pkg jumbo pasta shells
2 tbsp olive oil
1/2 cup finely chopped onion
3/4 lb bulk sweet Italian sausage
2 cloves garlic, minced (I used 4)
1 large egg
1 15-ounce container ricotta cheese
1 9-ounce frozen chopped spinach, thawed, squeezed dry
3/4 cup grated Parmesan cheese
4 ounce fresh mozzarella, grated
1/2 tsp each salt and pepper
1 32-ounce jar tomato sauce with basil

Bring pot of water to boil; add shells and cook according to package. Drain, rinse under cold water. Drain on paper towels.

Heat oil in large skillet on med-high heat; add onion and cook until soft, about 5 minutes. Add sausage, breaking up in small pieces with wooden spoon. Cook, stirring frequently, until sausage is no longer pink, about 5 minutes. Add garlic and cook 1 minute longer. Remove from heat.

Beat egg lightly in large bowl. Stir in ricotta, spinach, 1/2 cup Parmesan, mozzarella, salt, pepper, and cooled sausage mixture until well blended. Fill pasta shells with mixture.

Heat oven to 350. Spread 1 cup of tomato sauce in bottom of baking dish. Arrange shells in dish. Spread remaining sauce over shells. Cover with foil and bake for 30 minutes. Remove foil, sprinkle with remaining Parmesan. Bake another 10 minutes.

*I didn't realize I was short on Parmesan so I used mozzarella on top when I removed the foil.