In a medium saucepan combine the cream, broth, bay leaf, and salt and pepper. Add the onions and bring to a simmer over medium high heat. Lower the heat to maintain a simmer and cook for about 20 to 25 minutes, until the onions are tender and the liquid has thickened somewhat into a sauce. Remove the bay leaf, stir in the Parmesan (if using) and parsley, and turn into a serving bowl. Serve hot.