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How to Thicken French Onion Soup? 8 Easy Ways

If you want to thicken your French onion soup, you can add a bit of flour. Combine a couple of tablespoons of flour with a teaspoon of salt and whisk in about a quarter cup of water. Bring the mixture to a boil, then reduce the heat and simmer for about 10 minutes, until thickened. You can also add a little cream or milk.

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How to Thicken French Onion Soup

Many of us know French onion soup as that delicious soup served in a crock at the local diner or cafe.

But while many people are fans of this dish and order it every time they see it on a menu, some folks want a thicker, more filling version.

This article will cover how to thicken French onion soup for those who want an even richer and heartier meal.

How to Thicken French Onion Soup? 8 Easy Ways

How to Thicken French Onion Soup

There are a few ways to thicken French onion soup. You can use a roux, which is a mixture of flour and butter that is cooked until it turns a rich brown color.

You can also use a puree, which is a thickening agent that is made from mashed potatoes or egg yolks.

The third way to thicken French onion soup is to use a starch, which is a thickening agent that is made from cornstarch or tapioca starch.

Here are 8 of my favorite ways to thicken French onion soup:

1. Use Cornstarch to Thicken the Soup


This method works great for thickening soups like French onion soup.

To make your cornstarch-thickened soup, you’ll need two parts water and one part cornstarch. Make sure to mix these together thoroughly before adding to your soup.

Add your cornstarch mixture to your soup slowly and stir it constantly. It will take a few minutes for it to fully thicken.

Once the soup is thickened, add in any garnishes and seasonings that you would like to add. You can also garnish your soup with croutons if you prefer.

2. Potato Starch

Potato Starch

One of the best ways to thicken soups and sauces is to add potato starch. This is an excellent way to achieve the same consistency without using time-consuming methods.

Simply pour your soup or sauce into a small pot, add the starch and stir well.

This process is done in two steps. First, add the starch to your soup or sauce.

After 30 seconds or so, add a bit more of the starch. Continue stirring until the desired thickness is reached.

Since it requires no cooking, this is a much quicker method than simmering. It’s also much easier on the stomach and it’s a very healthy option.

3. Mix in A Small Amount of Flour


Adding a bit of flour to your soup is one of the best ways to thicken it.

The trick is not to add too much, which will give your soup a starchy taste. Instead, use just enough flour to form a paste with your onions.

It’s easy to mix into the liquid using a whisk and then let the mixture sit for at least 10 minutes to allow the flour to thicken the soup.

If your soup is too thick after this process, you can add a few tablespoons of milk to thin it out again.

4. Use a Starch to Thicken the Soup

Starch has been used for centuries to thicken foods. You can buy pre-made packets of thickening agent at most grocery stores.

If you’re using the packet method, it’s best to use only half the packet.

The goal here is to add enough starch to just start to thicken your soup.

A pinch of salt helps to ensure that your soup will be able to absorb the starch.

Be careful not to overdo it, as too much starch will result in a gummy texture.

5. Make a Roux, Then Add It to The Soup

If simmering your soup wasn’t enough to get that rich, thick consistency you’re looking for, you might need to add a thickening agent like roux.

If you’ve never made a roux before, it’s pretty easy! Roux is just a mixture of butter and flour and it’s most commonly used in French cooking.

To make your own roux to add to your onion soup, you’ll need equal parts butter and flour. Add your butter to a pan over medium heat and slowly sprinkle in the flour in small increments.

This ensures that the mixture turns out smooth. Continue whisking until the roux starts to bubble and you’re ready to add it to your soup!

When adding a roux, be sure to add in small increments while the onion soup is still warm so the roux can fully incorporate into it.

This method does require a bit more effort than just simmering, but the change in flavor will be very mild.

6. Egg Yolk

egg yolk

Adding just one egg yolk to the soup will be enough to thicken it up without changing the flavor.

Egg yolks are also a great way to add a little creaminess to your soup. Use the amount of yolk you’d normally use in an egg white omelet or a whole egg.

This technique works best when using a milder variety of onion, as well. A sweeter onion will cause the soup to break if you use the full amount of egg yolk.

7. Stir in Some Cream Cheese

Cream Cheese

Cream cheese is a great way to thicken and enrich your soup.

It’s rich and velvety and gives the soup that perfect finish. It also adds a mild tanginess to the soup so you don’t need to go overboard on the salt!

You can find cream cheese at just about any grocery store. Look for one with a minimum of 70% fat so that it doesn’t end up melting too fast when added to your soup.

8. Pureed Vegetables

Pureed Vegetables

For a quick and easy way to thicken your French onion soup, try making some homemade vegetable purees.

There’s really not much difference in taste between the soup and the pureed vegetables.

You can use these pureed vegetables in just about anything from dips to sauces to soups!

It’s also a good way to add extra nutrients to your diet.

How to Thicken French Onion Soup: 8 Easy Ways

Thickening French onion soup is very simple.
You will want to use either flour or cornstarch.
A teaspoon of each is all you need for thickening.
If you are looking for a thicker soup, then you may want to add a bit more than a teaspoon.
Prep Time3 minutes
Active Time3 minutes
Total Time6 minutes
Course: Soup
Cuisine: French
Keyword: How to Thicken French Onion Soup
Cost: 1


  • Use Cornstarch to Thicken the Soup
  • Potato Starch
  • Mix in A Small Amount of Flour
  • Use a Starch to Thicken the Soup
  • Make a Roux, Then Add It to The Soup
  • Egg Yolk
  • Stir in Some Cream Cheese
  • Pureed Vegetables
CEO at Happy Muncher | | Website | + posts

Hi, I'm Benjamin. I love cooking, long walks, and my girlfriend! Here you’ll find simple and delicious recipes that you can make in 30 minutes or less.