Sausage, Spinach and Cheese-stuffed Shells

1. Bring a large pot of salted water to a boil; add pasta shells and cook according to package instructions. Drain in a colander; rinse under cold water to stop the cooking. Drain shells on paper towels. 2. Heat oil in a large skillet on medium-high heat; add onion and cook until softened, about 5 minutes. Add sausage, breaking up into smaller bits with a wooden spoon. Cook, stirring frequently, until sausage is no longer pink, about 5 minutes. Add garlic and cook 1 minute longer. Remove pan from heat. 3. Beat egg lightly in a large bowl; stir in ricotta, spinach, 1/2 cup of the Parmesan cheese, mozzarella, salt, pepper, and the cooled sausage mixture until blended. Fill pasta shells with mixture. 4. Heat oven to 350 degrees F. Spread 1 cup of the tomato sauce over the bottom of a 3-quart baking dish. Arrange stuffed shells in dish. Spread remaining tomato sauce over pasta shells. Cover dish with foil; bake for 30 minutes, until hot and bubbling. Remove foil; sprinkle with remaining Parmesan cheese. Bake uncovered for 10 minutes longer.