Place onions, potatoes, carrots, celery, bay leaves & oil in large soup pot. Add just enough stock to cover. Bring to a boil & simmer over low heat for 10 minutes. Add the corn, tomatoes with hteir liquid & simmer for 10 minutes. Add the seasonings & simmer for another 10 minutes. Remove 3/4 cup of potatoes & mash well. Return to the pot with the 1 cup of stock. Stir well. Simmer for another 5 minutes, or until you are ready to serve it. Adapted from Nava Atlas, "Vegetariana"