Rinse and scrub clams several times to remove as much sand as possible. Discard any clams with a broken shell. Place clams in dishpan or sink and just cover with cold water. Sprinkle corn meal over all and leave to soak for 3 to 4 hours. Rinse one final time to remove any cornmeal adhering to clams and place them in a large pot. Add 2 1/2 quarts of water and bouquet garni. Bring to a boil covered and steam for 12 to 15 minutes or until clams are open. Remove pot from heat and allow to cool. Meanwhile, heat olive oil over medium heat in a 10 quart heavy Dutch oven and add salt pork. Cook, stirring frequently, until fat is rendered and pork pieces are brown and somewhat crisp. Remove pork with a slotted spoon, drain on paper towels and reserve. Add onions to pan and cook, stirring frequently until onions are soft and transparent (do not allow the onions to brown). While onions are cooking, remove clams from shells collecting liquid from clams in pot with cooking liquid. As clams are removed, rinse them in the cooking liquid to remove any additional sand and reserve. Pour cooking liquid through a strainer lined with 3 layers of cheesecloth and add to onions. Add potatoes, clam juice and if necessary, enough water to just cover potatoes. Cook for 20 minutes or until potatoes are tender. Add clams, half-and-half and pepper to taste. Cook until heated through and correct seasoning. Serve in mugs or bowls and sprinkle with reserved "cracklings." Pass oyster crackers separately.