Lightly fry the onions and pumpkin in the butter for about 5 minutes, do not colour. Add the stock, cover and simmer for about 1 hour, or until the vegetables are soft. Sieve or puree the soup in an electric blender and return it to the pan. Blend the flour with a little of the milk to a smooth cream. Add the rest of milk to soup and reheat. Stir a little of the soup into blended flour and milk and return this mixture to the pan; bring to the boil, stirring until it thickens, and cook for a further 2-3 minutes. Season, stir in the cheese and cream and sprinkle with parsley before serving.