Room-temperature egg whites will produce the most voluminous meringue. For just the right texture, whip the whites until they hold stiff, glossy peaks--but keep the mixture still spreadable enough that you can make decorative swirls in it as you top the pie.
Ice cream in a 500-degree oven? As long as it's bundled up in a thick layer of meringue, the outside caramelizes, and the inside (chocolate cake with chocolate ice cream) remains brr-illiantly chilly. Martha made this recipe on Martha Bakes episode 310.