Things You'll Need
Heavy bottomed frying pan
Experienced eaters and chefs alike know that corn tortilla soup traditionally has a thin, spicy broth. If you prefer a thicker soup (not just chunky) with more of a stew or chowder like consistency, any number of thickening methods can be employed without changing the delicious flavor. Corn starch, roux, tapioca flour, arrowroot flour, and potato starch can all be used safely with good results. Tortilla soup can also be reduced down through slow cooking if you hesitate to add additional carbohydrates.
Thickening With Roux
Melt 2 tbsp. butter in a frying pan over medium heat. Skim the froth from the top of the melted butter to clarify it.
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Blend 2 tbsp. flour in with the clarified butter and cook over medium heat until it forms a brown roux. Stir this mixture constantly as it cooks to prevent burning or scorching of the flour. When it is done cooking the roux will be a medium brown in color.
Incorporate this into the soup base near the end of the cooking process (after the vegetables have been fully cooked) and stir the soup until it has thickened as desired.
Thickening With White Wash
Measure 4 tbsp. flour into a medium sized mixing bowl.
Blend enough water with the flour to create a very thing paste. Whisk the mixture together until all of the lumps have been blended out.
Stir this mixture into the soup, near the end of the cooking process, and cook until the starchy flavor of the flour has been cooked out and the soup is thickened. If it is too thin repeat this process.
Thickening With Corn Starch or Arrowroot
Measure 3 tbsp. corn starch or arrowroot into a medium sized mixing bowl.
Blend 3 tbsp. liquid with the starch or arrowroot until all of the lumps are gone and it can coat the back of a spoon.
Stir the corn starch or arrowroot mixture into the soup, near the end of the cooking process, and cook until the soup has thickened as desired. The soup won't really begin to thicken until it has come up to a simmer. If it is still too thin you can add additional thickener.
Other thickening options can be used, but some of them will alter the flavor of the soup. Anything containing cream or eggs will thicken the soup, for example, but will turn it into more of a creamy chowder.
You can thicken the soup by reducing the broth and vegetable mixture before adding the avocado, cheese and tortilla strips. Cook the broth and vegetables over low to medium heat until the liquid has reduced by half. You can also puree a portion of the soup and add it back to the pot.
Chemical thickeners or gums can also be employed, but most ordinary kitchens do not contain these items.