Spread half the softened ice cream into a plastic wrap-lined 9x5-inch loaf pan, sprinkle with chopped chocolate bars or cookies, mini peanut butter cups, or anything else you like. Spread the second ice cream flavour on top, cover and return to the freezer until solid.
In the bowl of a double boiler (or a glass or stainless steel bowl that will fit over a saucepan of simmering water), whisk together the egg whites and sugar. Set over an inch or two of simmering water and whisk until the mixture is warm to the touch. Remove the bowl from the heat and beat with an electric mixer until stiff peaks form. If you want to broil the cake, preheat your broiler.
Remove the frozen cake and ice cream from the freezer, unwrap it on a serving plate and cover with meringue. Brown the surface with a culinary blowtorch or run it under the broiler for a minute or two, just until golden on the surface. Serve immediately. Serves 8-10.