Baked Rigatoni with Sausage and Mushrooms

4 cups hot water

4 tablespoons olive oil

4 large onion s, finely chopped

5 pounds hot Italian sausage s, casings removed

4 pounds button mushroom s, sliced

4 teaspoons chopped fresh rosemary

2 cups dry white wine

4 bay leaves

2 14-ounce cans beef broth

4 cups half and half 4 pounds rigatoni

6 cups freshly grated Parmesan cheese

Additional grated Parmesan cheese

Fresh rosemary sprigs (for garnish)