Put your slow cooker to work on everyone's favorite French bistro classic. Create meltingly sweet caramelized onions, no hands necessary. Top this delicious soup with mozzarella and gruyere for the perfect finishing touch.
Prep Time: 15 mins
Cook Time: 12 hours (largely hands off)
Yield: 9 cups soup (or 6 servings – 1 ½ cups each)
- 8 cups sliced onions (~ 6-7 large onions or 3 lbs)
- 4 TB unsalted butter, melted
- 2 teaspoons kosher salt
- ½ cup dry (fino) sherry
- 5 sprigs fresh thyme
- 1 bay leaf
- 3 cups chicken stock
- 3 cups beef stock
- 1 teaspoon sugar
- Additional salt and pepper to taste
- 6 slices Italian bread (cut ¼” thick on the diagonal)
- 1 cup shredded mozzarella cheese
- 1 cup shredded gruyere cheese
Combine onions, butter, and salt in a slow cooker. Cook on high for 8-9 hours or until onions are well browned. Add sherry and stir to combine. Continue to cook on high with lid off for 10-15 minutes to evaporate alcohol. Tie thyme and bay leaf with kitchen twine. Add herbs, both stocks, and sugar to onions, combine well, and cook, covered, on high, for 2-3 hours to marry flavors. Discard herb bundle. Season soup to taste with salt and pepper. Soup may be made up to 3 days before serving.
When ready to serve, heat oven to 400 degrees. Combine both cheeses in a medium bowl. Place baguette slices on a rack and toast for 4-5 minutes. Rewarm soup as needed and ladle into oven safe crocks, top each with one toasted baguette slice and 1/3 cup shredded cheese mix. Switch oven to broil setting and place crocks in oven to melt and lightly brown cheese. Serve immediately.
If you prefer, this soup can be finished on the stovetop after slow cooking onions. Simply transfer caramelized onions to a soup pot or Dutch oven to reduce sherry quickly on the stovetop. Add stock/herbs and bring to a simmer, uncovered, for 30 minutes.
If you don’t have oven safe soup crocks, melt the cheese directly on the baguette slice in the oven and transfer to top hot soup. Alternatively you can microwave crostini & cheese topped soup to melt cheese
Tip: Slicing onions pole to pole, along ridges, ensures they hold together for this preparation.
Originally developed for BedBathBeyond