The Dutch, who originally settled Manhattan Island in the seventeenth century, brought with them the recipe for this rib sticking pea porridge. Today, it still is served at the Netherland club in Manhattan. Other split pea soups pale in comparison.
In a non-reactive, large heavy stainless steel stockpot over medium heat, combine the split peas, 3 quarts cold water, the pig’s knuckle or 2 pig's feet, bacon, leek greens, onion, and the chunked carrot. Cut half of the celeriac into large chunks and add along with the bouquet garni. Bring to a boil over medium high heat. Reduce the heat, partially cover, and simmer, stirring occasionally, until the peas are very soft, about 2 hours.
Remove the pig’s knuckle; set aside to cool. Remove and discard the bouquet garni. Puree the remaining contents of the pot in batches in a food mill or processor until smooth. Return to the pot.
Cut the meat from the pig’s knuckle and add to the pot along with the white part of the leek, the chopped carrot, and the celery. Finely chop the remaining celeriac and add it to the pot. Simmer, stirring occasionally, until all of the vegetables are soft, about 30 minutes.
Stir in the kielbasa and cook until heated through, about 5 minutes. Season with salt and pepper to taste. Serve hot in soup bowls, with the chopped parsley on top. Serves 6 to 8.