Sausage Rigatoni Bake (Celise)

2 onions, sliced
1 lb. Italian sausage
1 jar pasta sauce
5 cups rigatoni pasta
2 cups mozzarella cheese
1/4 cup parmesan cheese
parmesan 2 tbsp parsley, fresh, chopped

Preheat oven to 400ºC. Cut sausage into 1-inch chunks; add to pan with onions and brown well on all sides, about 8 minutes. Drain off fat. Stir in pasta sauce. In large pot of boiling salted water, cook pasta for about 8 minutes or until tender but firm. Drain, reserving 1 cup (250 mL) of the cooking water. Return pasta to pot; add sauce and reserved cooking water.Combine mozzarella and Parmesan cheese; set 1 cup (250 mL) aside. Stir remaining cheese into pasta mixture. Pour into 13 x 9-inch (3 L) glass baking dish, pressing pasta to submerge. Sprinkle with reserved cheese and parsley.Bake, covered, in oven for 30 to 45 minutes; uncover and continue for another 15 minutes or until golden.(Make ahead: Let cool in refrigerator; cover and refrigerate for up to 1 day. Or overwrap with heavy-duty foil and freeze for up to 2 weeks; thaw in refrigerator for 48 hours.)