Check for and discard any pebbles that may have been packaged with the peas and then rinse them in a large strainer and set them aside.

Add the water to a Dutch oven or large heavy-bottomed soup pot and add the ham hock and salt. Bring to a boil, reduce to simmer and cook for 1hour. Remove the ham hock and discard. With a strainer, skim any scum and fat from the broth and measure the remaining broth adding additional water to total 8 cups of liquid.

Add the green peas, onions, thyme bundle, and bay leaves to the measured liquid. Turn the heat to medium-high and bring the soup to a boil. Cook for 10 minutes. Reduce the heat to low and simmer for one hour.

Add the chicken stock and stir in the chopped carrots and celery. Return to a boil, reduce the heat to low, and simmer for an additional 45 minutes. Remove the bay leaves and what is left of the tied thyme bundle and discard.

If you want a smooth, thick soup, puree it in a blender. Working in batches, add the soup to a food processor or blender, being careful not to overfill with the hot soup. When all the soup has been processed to a creamy consistency return it to the soup pot and bring it to a boil.

Remove from the heat and serve with a dollop of sour cream and a sprig of thyme in each bowl as a garnish.