5. Thicken Soup With Flour or a Starch
A “slurry” is simply a mixture of starch, such as flour, cornstarch, potato starch, or tapioca starch, whisked into water. The slurry is then added to a soup or sauce to thicken it. The reason to make a slurry rather than whisking starch directly into soup is to avoid clumping, which will most certainly happen if you sprinkle starch directly into your simmering pot. A slurry is best deployed near the end of cooking a soup, making it a good choice for when you realize that your chowder isn’t as thick as you like it or when you want your soup to have a little more body.
Make a slurry by whisking a tablespoon of starch into a quarter-cup of cold water until smooth, then add some of the broth from your soup pot and whisk to combine and help warm the slurry. Then pour it into your soup pot and stir it in. It should start thickening instantly, but be sure to let the soup come to a boil to get the full thickening power of the starch. Note: When using all-purpose flour, whisk extra well to avoid lumps, and be sure to let the soup boil for at least a full minute to thicken.