Peel, and clean nicely, twelve large potatoes; cut them into balls with a Parisian potato-scoop, then place them in a saucepan, covering them with water containing a pinch of salt. Cook for fifteen minutes; then strain them and place them in another saucepan with an ounce of fresh butter and a pinch of chopped parsley. Warm them well for five minutes, and add the juice of half a lemon before serving.