- 4 tbsp.(1/2 stick) unsalted butter
- 3 lb.(about 6 medium-size) onions, thinly sliced
- Kosher salt
- 1/4 c.dry white wine
- 2 tbsp.dry sherry
- 1 tbsp.all-purpose flour
- 6 c.beef broth
- 4thick slices crusty bread
- 4 oz.Gruyère cheese, grated (about 1 cup)
- Step 1Melt butter in a large Dutch oven or pot over medium heat. Add onion and season with salt. Reduce heat to medium-low and cook, stirring often at first and then only occasionally, until onions are golden brown and caramelized, 1 hour to 1 hour 15 minutes.
- Step 2Add white wine and dry sherry and bring to a boil. Add flour and cook, stirring, until thickened, 1 to 2 minutes. Stir in broth and let simmer 10 minutes. Season with salt.
- Step 3Heat oven to broil. Place 4 broiler-safe bowls on a sheet tray and fill with soup. Top each with a slice of bread (trimming to fit, if necessary) and cheese, dividing evenly. Broil until cheese is golden brown, 1 to 2 minutes. Serve immediately.