Next add the cornstarch slurry; make sure the cornstarch and water is mixed well, as the cornstarch settles very quickly. Stir the soup continuously as you drizzle in the slurry, or you’ll get unpleasant clumps of cooked starch in your soup. Use more or less starch if you like a thicker or thinner soup. You can also add the starch in a couple small batches, let the soup simmer for a couple of minutes, then check to see if the consistency is to your liking.