Fill a large soup pot with the 2 quarts of water and bring to a  boil. Add the chicken base (or shrimp base), celery, onion and potatoes. Reduce heat to medium-high and continue cooking until the vegetables are cooked, 15 to 20 minutes.

Add the shrimp and return to a boil. Reduce the heat and bring to a simmer. In a small bowl add the cornstarch to a little bit of cold water and stir until totally dissolved. Slowly add the conrnstarch mixture to the soup, stirring contiuously until the soup thickens to the desired consistency.

Season with pepper, garnish with parsley (optional) and serve hot.