Peel ten medium-sized, sound, freshly cooked pctatoes ; cut them into small slices, lay them in a salad-bowl, and add a finely chopped onion and a teaspoonful of chopped parsley. Season with a pinch and a half of salt, one pinch of pepper., half a gill of vinegar, and three tablespoonfuls of sweet oil, then mix thoroughly and gently with a spoon and fork, without breaking the potatoes. Wipe the bowl neatly with a napkin, and send the salad to the table.