Wash, clean, and chop the potatoes, onions, carrots, and celery. Add to the water and boil for 20 min. Add salt and tomatoes (if you are using ripe tomatoes, pierce with fork) and cook for 30 to 45 min. Remove from the heat. Pass all the vegs. through a strainer or puree machine or blender, then return to the pot. Add a little pepper and stir in the shortening or serve the soup and add oil at the table. Serve with croutons.