Cut the top 1/4 off 4 pumpkins, reserving the lids. Cut the remaining 4 pumpkins in half. Reserve seeds from 2 pumpkins. Bake the pumpkins, cut side down, on lightly oiled baking sheets in a preheated 350 oven for 40 min or until they are tender. When they are cool enough to handle, scrape all the pulp out of the halved pumpkins. Scrape most of the pulp out of the remaining pumpkins, leaving just enough in each pumpkin so that it retains its shape.
In a skillet cook the onion in butter over low heat, stirring, until the onion is softened. Add the pumpkin pulp, the chicken stock and the water and simmer the mixture for 20 minutes. Puree the mixture in batches in a blender and transfer it to a saucepan. Stir in salt and pepper to taste and water to thin the soup if necessary. Reduce oven heat to 250. In a bowl, toss the reserved seeds with the oil and salt to taste and spread them out on an ungreased baking sheet. Bake the seeds in the middle of the oven, stirring occasionally, for 1 hr to 1 1/2 hrs or until they are golden and crisp.
Heat the soup and warm the hollowed out pumpkin shells in the oven. Arrange the shells in 4 soup plates, fill each shell with some of the soup and ladle some additional soup around each shell. Sprinkle some crumbled blue cheese and toasted pumpkin seeds on top of each soup and serve with the lid on top.