Ingredients
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1 tablespoon unsalted butter
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3 large yellow onions, thinly sliced
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1 teaspoon kosher salt
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1 garlic clove, minced
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¼ teaspoon granulated sugar
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¼ teaspoon dried thyme
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1 bay leaf
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4 cups low-sodium beef broth
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2 teaspoons Worcestershire sauce
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1 cup French or ciabatta bread cubes
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1 cup grated Swiss cheese
Instructions
Melt the butter in a large saucepan or Dutch oven over medium heat.
2. Caramelize the Onions
Add the sliced onions and kosher salt. Cook for about 30 minutes, stirring occasionally, until the onions soften and turn golden brown. Adjust the heat as needed to prevent burning. The slow cooking develops the soup’s signature sweetness and rich flavor.
3. Add the Aromatics
Stir in the garlic, sugar, dried thyme, and bay leaf. Cook for another 10 minutes, stirring occasionally, until the onions deepen in color and the garlic becomes fragrant.
4. Simmer the Soup
Pour in the beef broth and Worcestershire sauce. Bring the mixture to a boil, then reduce the heat to low and simmer for about 10 minutes, until the onions are very tender and the flavors come together.
5. Toast the Bread
While the soup simmers, preheat the oven broiler. Spread the bread cubes on a baking sheet and broil for 3–5 minutes, watching closely, until crisp and golden. Set aside.
6. Assemble the Bowls
Remove the bay leaf from the soup. Ladle the hot soup into oven-safe bowls and place them on a sturdy baking sheet. Top each bowl with toasted bread cubes and a generous handful of grated Swiss cheese.
7. Broil Until Gooey
Place the bowls under the broiler for about 2 minutes, or until the cheese melts and becomes bubbly. Watch carefully, as broilers can brown cheese quickly. Use oven mitts to remove the bowls and let them cool briefly before serving.
Notes
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Take your time with the onions: Proper caramelization is the key to deep, sweet flavor. Avoid rushing by turning the heat too high.
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Stir and scrape: As the onions cook, scrape up the browned bits from the bottom of the pot to build flavor.
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Watch the garlic: Add it after the onions have softened to help prevent it from burning.
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Toast the bread well: Crisp bread holds up better under the soup and cheese.
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Choose a good melting cheese: Swiss works well, while Gruyère offers a richer, nuttier flavor.
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Use oven-safe bowls only: Regular bowls may crack under the broiler’s intense heat.
