Soups, Stews & Chili

French Onion Potato Soup with Melted Swiss Cheese

By Clara ·
November 1, 2026

The onions begin as a heap in the Dutch oven, then slowly soften and shrink until they’re deeply golden. It takes patience, but that long, steady cook is what gives French Onion Potato Soup with Melted Swiss Cheese its rich onion flavor instead of a sharp, raw edge.

I stir the onions often and keep an eye on the heat. Once they’re soft and browned, a little flour goes in before the broth. Whisking the broth in gradually helps it blend smoothly, while the potatoes simmer right in the same pot and soak up the beefy, thyme-scented broth.

At the end, shredded Swiss melts into a bubbling cap over each serving. Underneath, the soup is thick with tender potato and sweet onion, with enough broth to make every spoonful feel warming and satisfying.

Why the Flour Goes In Before the Broth

Adding the flour while the onions are still in the pot gives it a chance to coat them and cook briefly in the butter before any liquid goes in. That small pause matters: flour stirred straight into a full pot of broth is more likely to leave little lumps that are hard to whisk out once the potatoes are in the way.

After the flour cooks for a minute, pour in the low-sodium beef broth gradually while whisking. The liquid loosens the flour from the onions and blends it into the soup base, so the broth thickens evenly rather than turning pasty in spots. It won’t become a heavy cream-style soup; the potatoes add body as they simmer, and the broth still flows easily around them.

Keep the whisk moving as the broth goes in, especially across the bottom and corners of the Dutch oven. Once the liquid is smooth, add the potatoes and seasonings, bring everything to a boil, then lower the heat to simmer. The order lets the flour do its job before the potatoes need attention.

What the Onions, Yukon Golds, and Swiss Each Bring

• Yellow onions — Their sweetness deepens as they cook, creating the soup’s main flavor. Choose firm onions without soft spots, then slice them thinly so they soften evenly in the pot.
• Unsalted butter and kosher salt — Butter carries the onion flavor and gives the onions a rich base. Unsalted butter lets the divided kosher salt season the soup without relying on the salt level of the butter.
• All-purpose flour — It gives the broth gentle body without turning it into a thick gravy. Stir it through the onions so there are no dry pockets before adding broth.
• Low-sodium beef broth — This brings savory depth and keeps the soup in the French onion family. Low-sodium broth is useful here because the soup also gets kosher salt and a salty cheese topping.
• Yukon Gold potatoes — Their creamy texture suits this broth-based soup, and the peeled half-inch cubes cook evenly while holding their shape. Keep the pieces close in size so they become tender together.
• Dried thyme and bay leaf — These give the broth a quiet herbal note without competing with the onions. The bay leaf needs to come out before the soup is ladled into bowls.
• Shredded Swiss cheese — Swiss melts into a smooth, savory topping that balances the sweetness of the onions. Spread it evenly over the bowls so each serving gets a bubbling layer instead of a few clumps.

Taking the Soup from Slow-Cooked Onions to a Bubbling Cheese Cap

Let the onions soften and turn deeply golden

Melt the butter in a 5- to 6-quart Dutch oven over medium heat, then add the thinly sliced onions and 1 teaspoon of kosher salt. Cook for 35 to 45 minutes, stirring often, until the onions are deeply golden and soft. If the edges begin to scorch, lower the heat rather than letting dark spots spread through the batch. The onions should look reduced and tender, not crisp or blackened.

Coat the onions before adding broth

Stir in the flour and cook for 1 minute, keeping the onions moving so the flour coats them evenly. Gradually whisk in the beef broth, scraping across the bottom of the pot as you pour. Add the cubed potatoes, dried thyme, bay leaf, remaining kosher salt, and ground black pepper. A gradual pour gives you a smooth base before the vegetables fill the pot.

Simmer until the potato centers are tender

Bring the soup to a boil, then reduce the heat and simmer partially covered for 15 to 20 minutes. Check a potato cube with a fork; it should be very tender all the way through, without a firm center. If the potatoes still resist, keep the soup simmering until they soften. Remove the bay leaf before serving.

Melt the Swiss under the broiler

Preheat the broiler with a rack about 6 inches from the element. Set four broiler-safe bowls on a rimmed baking sheet, ladle in the soup, and top the bowls evenly with the shredded Swiss. Broil for 1 to 3 minutes, watching closely until the cheese is melted and bubbling. Use bowls marked broiler-safe; ordinary serving bowls can crack under direct high heat.

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Questions That Come Up While the Soup Cooks

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 mins

Cook Time 1 hour hr 1 minute min

Resting 2 minutes mins

Total Time 1 hour hr 23 minutes mins

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.