1. Halve each onion through the root. Peel away the skins. Thinly slice the onions into half-moons.  Cut the onion slices in half. You should have at least 6 cups of sliced onions. 

2. Place the butter and oil in a Dutch oven or large sauté pan with deep sides over medium-low heat. Add onions, saute 10 minutes. Cover pan, reduce heat to low, and cook for 15 minutes. Uncover. The onions should have wilted down somewhat. Stir in the salt, a generous quantity of black pepper, and the sugar (this helps the onions caramelize).

3. Turn the heat up to medium and cook uncovered, stirring every few minutes, until the onions are deeply browned, about 10 minutes. Add flour to the caramelized onions and cook, stirring for about 1 minute.

4. Add the hot broth, wine and worcestershire sauce to the caramelized onions and bring to a boil. Lower the heat and partially cover the pan. Cook gently over low heat until the broth is slightly reduced, about 30 minutes.

5. Arrange a rack in the middle of the oven and heat to 350°F. Divide the soup between small but deep oven-safe bowls. Top each with a slice or two of toasted baguette and sprinkle grated cheese in a thick layer over the bread and up to the edge of the bowl.

13. Place the bowls on a rimmed baking sheet or in a casserole dish. Turn the oven up to broil. Broil until the cheese is melted, browned and bubbling, 1 to 3 minutes. Remove carefully from the oven and let cool for a few minutes before serving on heatproof dishes or trivets. Serve with freshly ground pepper and minced fresh onion or shallot.