Pare one nice tart apple, core and stand it in an individual baking dish; fill the core space with a teaspoonful of granulated sugar, add a half cupful of water, cover and bake until the apple is perfectly tender. Beat the white of one egg until light and dry, add a level tablespoonful of powdered sugar, and beat again. Take the apple from the oven, cover it thickly with the meringue, dust with powdered sugar and return to the oven until a golden brown. Serve hot or cold.