INGREDIENTS:

• 4 large yellow onions, halved and thinly sliced
• 4 Tbs. (1/2 stick) (2 oz./60 g) unsalted butter, melted
• Kosher salt
• 1/4 cup (2 fl. oz./60 ml) dry white wine
• 1/4 cup (2 fl. oz./60 ml) medium-dry sherry
• 5 cups (40 fl. oz./1.25 l) beef stock
• 2 fresh thyme sprigs
• 12 baguette slices, cut on the diagonal
• 1/2 cup (2 oz./60 g) grated Gruyère cheese
• 3 Tbs. finely snipped fresh chives

DIRECTIONS: 1) To make the caramelized onions, the night before serving, put the onions in a slow cooker, add the butter and 1 tsp. salt, and toss to coat the onions evenly. Cover and cook on the low setting for 10 hours, stirring once in the first few hours if possible. 2) The next morning, stir the onions, re-cover and cook on the high setting until the onions are golden and most of the liquid has evaporated, 1 to 2 hours. If the liquid has not evaporated, set the lid ajar for 1 to 2 hours to evaporate the liquid while the onions continue to cook. (The onions can be caramelized in advance. Let cool to room temperature, then transfer to an airtight container and refrigerate for up to 3 days or freeze for up to 3 months.) 3) When the onions are ready, add the white wine, sherry, stock and thyme to the onions and stir well. Cover and cook on the low setting for 5 hours. The onions should be very soft. 4) Just before the soup is ready, preheat the broiler. Arrange the baguette slices on a rimmed baking sheet and top them with the cheese, arranging it in an even layer. Broil until the tops are golden, about 30 seconds. 5) Remove and discard the thyme sprigs from the soup. Ladle the soup into shallow bowls, top each serving with 2 or 3 Gruyère toasts, sprinkle with the chives and serve.