Wash the dried peas in cold running water and place them in a 2-3 quart saucepan. Cover with 5 cups cold water and bring to a boil over high heat. Boil briskly for 2 or 3 minutes then turn off the heat and let the peas soak in the water for an hour. Skim off any pea husks that may have risen to the surface, add the finely chopped onion, the whole onion, salt pork, marjoram and thyme and again bring to a boil. Immediately lower heat and simmer with pot partially covered for about 1 1/4 hours or until peas are quite tender but have not fallen apart. Remove the whole onion and the salt pork from the soup and cut the pork in slices about 1/4" thick. This may be served in either of two variations. Place a few slices of pork in individual serving bowls. Season the hot soup with salt to taste and ladle it over the pork. Or, if you prefer, serve the soup alone, accompanied by a separate place of the sliced salt pok and spicy brown mustard. Note: If domestic yellow split peas are used, they need not be soaked for an hour. Wash them carefully, cover them with 4 cups cold water and proceed with the recipe as above. They will take somewhat less time to cook than the Swedish peas.