Preheat oven to 400°. In pan, cook onions in butter until tender. Pour in bread crumbs, cook for 3 minutes. Cut top off of pumpkin, scrape out seeds and strings. Rub inner flesh of both pumpkin shell and cover with soft butter. Set pumpkin on pizza pan. Pour crumb mixture in pumpkin, stir in grated cheese, and fill pumpkin within 2 inches of its top with hot chicken stock. Season to taste with salt, pepper, and sage. Set pumpkin on lower shelf of oven and cook for about 1½ hours. DO NOT OVERCOOK OR THE PUMPKIN WILL COLLAPSE! Take pumpkin out of the oven. Before serving, bring cream almost to a simmer. Gently stir into soup, followed by the chopped parsley. At the table, ladle the soup into hot bowls, scraping off some of the flesh from inside the pumpkin.