Preheat oven to 350 degrees F.
Cook rigatoni in salted water according to package directions until 1 minute shy of al dente – don’t overcook because it will continue to cook in the oven. Strain and rinse with cold water. Meanwhile, heat oil in a large Dutch oven over medium-high heat. Once hot, add the onions and cook for 3 minutes. Add sausage and cook until almost cooked through. Add the bell peppers, garlic and optional red pepper flakes and cook for an additional 2-3 minutes or until the onions are softened. Discard excess grease (if there is any). Stir in crushed tomatoes, tomato sauce, bouillon, sugar, bay leaf and all seasonings.
Cover, leaving about a 1-inch gap, and gently simmer for 8 minutes, stirring occasionally. Discard the bay leaf.
Stir in the heavy cream, followed by the rigatoni. Stir until pasta is completely coated. Taste and season with additional salt, pepper and/or red pepper flakes to taste. Add to a lightly greased 9x13 baking dish. Top with Parmesan and mozzarella. Cover with foil and bake at 350 degrees F for 30 minutes or until cheese is melted. Remove the foil and bake a few more minutes for toasted cheese if desired. Garnish with fresh parsley (optional).