Step 1

Halve and peel the onions. Halve each onion through the root. Peel away the skins.

Step 2

Thinly slice the onions. Thinly slice the onions into half-moons.

Step 3

Cut the half moon slices in half. Cut the onion slices in half. You should have at least 6 cups of sliced onions. But don't worry too much about quantities with this recipe; if you have an extra onion to use up, throw it in!

Step 4

Melt the butter with the oil. Place the butter and oil in a Dutch oven or large sauté pan with deep sides over medium-low heat.

Step 5

Add the onions. After the butter foams up and then settles down, add the onions and stir to combine.

Step 6

Cover and cook for 15 minutes. Cover the pan, reduce the heat to low, and cook for 15 minutes.

Step 7

Season the onions. 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).

Step 8

Cook the onions for 40 minutes to 1 hour. Turn the heat up to medium and cook uncovered, stirring every few minutes, until the onions are deeply browned. Turn down the heat if the onions scorch or stick to the pan; the browning doesn't come through burning, but through slow, even caramelization.

Step 9

Heat the broth. As the onions approach a deep walnut color, heat the broth in a separate pot.

Step 10

Add the flour. Add the flour to the caramelized onions and cook and stir for about 1 minute.

Step 11

Add broth and simmer for at least 1 hour. Add the hot broth to the caramelized onions and bring to a boil. If using wine, add this now too. Lower the heat and partially cover the pan. (If you want to add other aromatics such as herbs or spices, do so now.) Cook gently over low heat until the broth is slightly reduced, at least 1 hour.

Step 12

Taste and season. Taste and season with more salt and pepper if needed. Add a finishing splash of brandy, if desired!

Step 13

Top with toast and cheese. 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.

Step 14

Bake for 20 to 30 minutes. Place the bowls on a rimmed baking sheet or in a casserole dish. Bake until the cheese is completely melted, 20 to 30 minutes.

Step 15

Broil until the cheese is browned. Turn the oven up to broil. Broil until the cheese is 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, which provides a welcome bite in contrast to the very sweet and mellow soup.