How To Slice Onions For French Onion Soup?

Slicing onions for French onion soup requires a certain level of finesse, as this ingredient can make or break the flavor of your soup. Slice onions thickly, about 1/4 inch. Knowing how to dice and slice an onion properly will ensure you get the most out of each flavorful morsel.

Why Onion Slicing Matters For French Onion Soup?

Why Onion Slicing Matters For French Onion Soup
Onion Slicing Matters For French Onion Soup
  • Flavor: The way you slice your onions can affect the flavor of your French onion soup. Uniformly sliced onions cook more evenly, allowing for the development of rich, caramelized flavors that are the hallmark of a great French onion soup.
  • Texture: Uniformly sliced onions also contribute to a better texture in the soup. Properly sliced onions will maintain their shape during the long cooking process, providing a pleasant mouthfeel.

How Thick Should Onions Be For French Onion Soup?

Thickness is a personal preference and will depend on the texture you’re looking for in your soup. Generally, it is recommended to cut onions into thick slices of about 1/4-inch. This size slice will hold up during cooking and caramelize while still melting to create a creamy base for the soup. If you prefer a chunkier soup, opt for thicker slices. If a smoother soup is desired, thin slices of 1/8 inch or less will do the trick.

How To Choose The Best Onions For Your Soup?

Sweet onions
Sweet onions
  • Sweet onions are best for French onion soup, as they are less pungent and add a natural sweetness that enhances the soup’s flavor.
  • When possible, try to find freshly harvested sweet onions from local growers. If not available, look for red or yellow onions—they should still work well.
  • Avoid cooking or storing onions, as they tend to be too strong for French onion soup and can overpower the other flavors.
  • Choose firm onions with tight skin, avoiding soft or spongy ones that may have started to rot.
  • Once you’ve picked the right onions, rinse and peel them before slicing.

How To Slice Onions For French Onion Soup?

Step 1. Start by washing the onions and peeling off their skins.

Step 2. Slice off the ends of the onion, then cut the onion in half from top to bottom.

Step 3. Place each half cut-side down and carefully slice into thin slices, keeping your fingers away from the blade of your knife.

Step 4. Make sure to keep the slices as even in thickness as possible so they will cook evenly when you are making your soup.

Step 5. Separate the onion slices into individual rings, and prepare and cook your French onion soup according to the recipe instructions!

Slicing Onions For French Soup In Slicer?

Step 1. Set your onion on a cutting board and cut off the top and bottom ends. Then, peel off the outer skin of the onion.

Step  2. Slice the onion from top to root in half, leaving you with two flat sides.

Step  3. Place one of the halves on its flat side and make evenly spaced, horizontal cuts parallel to the cutting board.

Step 4. Turn the onion 90° and make vertical slices in the same spacing as before. The resulting pieces should be uniformly sized small cubes.

Step 5. Use a slicer or mandolin set over the smallest cutting size to achieve a finer mince for your French onion soup. This will give you the thinnest slices possible and make for a smoother soup consistency.

Step 6. Place the sliced or minced onion in a bowl of cold water for 5-10 minutes to help reduce the strength of the onion’s flavor and aroma.

How To Make A French Onion Soup?


  • 4 large yellow onions, sliced
  • 4 tablespoons unsalted butter
  • 1 tablespoon olive oil
  • 1 teaspoon sugar
  • 2 cloves garlic, minced
  • 6 cups beef broth
  • 1 cup white wine
  • 2 bay leaves
  • 2 sprigs of fresh thyme
  • Salt and freshly ground black pepper to taste
  • 1 baguette, sliced
  • 2 cups grated Gruyère cheese


Step 1: Melt the butter and olive oil over medium heat in a large pot. Add the onions and cook, stirring occasionally, for 20-25 minutes until they are soft and golden brown. Stir in the sugar and cook for an additional 5 minutes.

Step2: Add the garlic and cook for 1 minute. Pour in the beef broth, white wine, bay leaves, and thyme—season with salt and pepper. Bring to a boil, reduce the heat, and simmer for 30-40 minutes.

Step 3: Preheat the broiler. Toast the baguette slices until golden brown.

Step 4: Ladle the soup into oven-safe bowls. Top with toasted baguette slices and a generous amount of Gruyère cheese. Place the bowls under the broiler until the cheese is melted and bubbly.

Slicing Onions For French Soup In Food Processor

Step 1. Peel and halve the onion(s).

Step 2. Place half (or quarters, depending on size) of the onion into the food processor bowl, cut side facing down.

Step 3. Fit the lid to the food processor and pulse a few times for about 2-4 seconds until you get desired thickness of slices.

French Onion Soup: Nutritional Information And Health Hacks

  • Lower the fat: To reduce the fat content of your French onion soup, use a low-fat or vegetable broth instead of regular beef stock. You can also opt for reduced-sodium versions of both stocks to cut back on salt.
  • Lower the sodium: One of the keys to healthy French onion soup is to reduce the sodium content. To do this, use low-sodium broth or a combination of regular broth and water. If desired, add herbs and spices for flavor instead of relying on salt. You can also reduce the cheese used in the recipe, as cheese is often high in sodium.
  • Use the right pan: For best results, use a large oven-safe skillet or Dutch oven to make French onion soup. This pan distributes heat evenly and allows the onions to caramelize properly. In addition, an oven-safe pan makes it easy to transfer your soup to the oven for baking.

How To Slice Onions Without Crying

Chill the Onions: Place the onions in the refrigerator for about 30 minutes before slicing. This reduces the release of the enzyme that causes tearing.

Use a Sharp Knife: A sharp knife will cause less damage to onion cells, releasing fewer irritating compounds.

Ventilation and Breathing Techniques: Ensure proper ventilation in your kitchen and try breathing through your mouth while slicing onions to reduce the impact of irritating compounds on your eyes.


Can I use red onions for French onion soup?

While red onions can be used, they have a stronger, more pungent flavor that may not be as suitable for French onion soup as yellow or sweet onions.

Can I freeze French onion soup?

Yes, you can freeze the soup without the bread and cheese toppings. Reheat the soup on the stove, then add the toppings and broil as directed.

Can I make French onion soup in a slow cooker?

Yes, after caramelizing the onions on the stovetop, transfer them to a slow cooker along with the remaining soup ingredients. Cook on low for 6-8 hours or high for 3-4 hours.

How can I make my French onion soup gluten-free?

Use a gluten-free baguette or omit the bread entirely. Ensure the broth and other ingredients are gluten-free as well.

How long does French onion soup last in the refrigerator?

French onion soup can be stored in the refrigerator for up to 4 days. Reheat on the stove and add fresh bread and cheese toppings before serving.

What’s the difference between Onion soup and French Onion soup?

Onion soup is a flavorful broth that typically contains onions, herbs, and spices. French onion soup has an additional layer of complexity thanks to the caramelized onions that give it a sweeter flavor.


How To Slice Onions For French Onion Soup - Infographics
How To Slice Onions For French Onion Soup – Infographics

Slicing onions for French onion soup can be a tricky task. If you’re not careful, you can easily end up with unevenly sliced onions that don’t cook properly in the soup. However, if you take your time and use a sharp knife to slice the onions slowly and at an angle, you’ll be able to get even slices for the perfect French onion soup. Remember always to use caution when cutting onions, as they can be slippery and sharp. With these tips, you’ll have a delicious French onion soup in no time.