Combine peas, water, ham shank or hocks or bacon, onion, bouillon and seasonings. Cover and simmer 1 1/2 hours. If using shank, remove shank, trim meat from bone, and return to pot. Stir in carrots, celery and potatoes. Cover and simmer 2-2 1/2 hours. (Time may vary - basically just need enough time for the split peas to soften completely). Add a small amount of flour if desired to thicken (I've already reduced the water dramatically from the original recipe, to make the soup thick, as we like it).
(Another variation soaks the peas overnight, uses less water as a result, melts in 3 tablespoon butter and 3 tablespoons flour, and adds milk.)