1/4 cup Dry sherry, vermouth, or white wine optional
Bay leaf or thyme sprigs optional
2 quarts Stock (beef, chicken, or vegetable) the more robust the better
Freshly ground black pepper
1 Garlic clove
Bread slices One (3/4- to 1-inch) thick slice of bread for each bowl of soup
1/4 cup Gruyere, comte, or a mix of gruyere and parmesan grated per toast
Equipment
5- to 6-quart saucepan or Dutch oven
Broiler or oven
Baking sheet with foil
Directions
Melt butter in the bottom of a 5- to 6-quart saucepan or Dutch oven over medium heat. Add the onions, toss to coat them in butter and cover the pot. Reduce the heat to medium-low and let them slowly steep for 15 minutes. They don’t need your attention.
Uncover the pot, raise the heat slightly and stir in salt. Cook onions, stirring every 5 minutes for about 40 to 90 minutes longer. If your onions are browning before 40 minutes are up, reduce the heat to low, and if that’s still cooking too fast, try a smaller burner.
When onions are caramelized, add sherry or vermouth, if using, and scrape up any onions stuck to pan. Cook until it disappears. Add stock, herbs (if using), and freshly ground black pepper and bring soup to a simmer. Partially cover pot and simmer for 15 to 20 minutes. Taste and adjust seasoning as needed; discard thyme sprigs and bay leaf if you used them.
While soup is finishing, heat your broiler, and if you don’t have a broiler, heat your oven as hot as it goes. If your bread is not already stale, toast them lightly, until firm. Rub lightly with a raw garlic clove. Line a baking sheet with foil and arrange soup bowls/vessels on top.
Ladle soup into bowls. Fit a piece of toast onto each. Sprinkle with cheese. Run under broiler until cheese is melted and brown at edges. Garnish with herbs. Serve immediately.