The perfect pumpkin soup has a beautiful, velvet texture, but if yours is too thick or thin it is easy to fix. TOO THICK: This is an simple fix, simply thin the soup with a little more stock or water and blend until smooth. TOO THIN: The easiest and quickest way to thicken a watery soup is to use cornstarch/cornflour. Mix 2 tsp of cornstarch/cornflour with 4 Tbsp cold water in a small bowl. Heat the soup until it is nearly boiling, then drizzle in the cornstarch mixture a little at a time, stirring until the desired consistency is reached.