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French Onion Potato Soup with Melted Swiss Cheese

French onion potato soup is simmered until the Yukon Gold potatoes are very tender, then topped with Swiss cheese and broiled until bubbling. Deeply golden onions give this hearty soup its rich flavor.
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Prep Time 20 minutes
Cook Time 1 hour 1 minute
Resting 2 minutes
Total Time 1 hour 23 minutes
Servings: 4 servings
Course: Dinner
Cuisine: French
Calories: 630
Ingredients Equipment Method Notes

Ingredients
  

For the soup
  • 3 tbsp unsalted butter
  • 2 lb yellow onions halved and thinly sliced
  • 1.5 tsp kosher salt divided
  • 2 tbsp all-purpose flour
  • 6 cups low-sodium beef broth
  • 1.5 lb Yukon Gold potatoes peeled and cut into 1/2-inch cubes
  • 1 tsp dried thyme
  • 1 bay leaf
  • 0.5 tsp ground black pepper
For the topping
  • 6 oz Swiss cheese shredded

Equipment

  • 1 5- to 6-quart Dutch oven
  • 1 rimmed baking sheet
  • 4 broiler-safe bowls

Method
 

Cook the soup
  1. Melt the butter in a 5- to 6-quart Dutch oven over medium heat.
  2. Add the onions and 1 teaspoon of the salt; cook, stirring often, for 35 to 45 minutes, until deeply golden and soft, lowering the heat if they begin to scorch.
  3. Stir in the flour and cook for 1 minute.
  4. Gradually whisk in the beef broth.
  5. Add the potatoes, thyme, bay leaf, remaining 1/2 teaspoon salt, and pepper.
  6. Bring the soup to a boil.
  7. Reduce the heat and simmer partially covered for 15 to 20 minutes, until the potatoes are very tender.
  8. Remove the bay leaf.
Melt the cheese
  1. Preheat the broiler with a rack about 6 inches from the element.
  2. Ladle the soup into 4 broiler-safe bowls set on a rimmed baking sheet.
  3. Top the soup evenly with the Swiss cheese.
  4. Broil for 1 to 3 minutes, until the cheese is melted and bubbling.
  5. Let the bowls stand for 2 minutes before serving.

Notes

For the deepest onion flavor, cook them slowly and lower the heat if they start to scorch. Refrigerate leftovers for up to 3 days; freezing is not recommended because the potatoes may become grainy. For a vegetarian variation, use vegetable broth instead of beef broth.