Place the cake circle on a heat-proof plate. Optionally, sprinkle with liquor of choice or cool coffee.
Spread the softened ice cream on the cake in a tall dome shape. It's nice to use two different kinds for a surprising effect. Freeze until the ice cream is hard, about 2 hours.
Cover the cake and ice cream dome completely in a thick layer of Swiss Meringue. Make little peaks all over with the spatula to create a prickly effect, or create swirls with the back of a spoon. At this point, the dessert can be re-frozen for few hours before baking.
Shortly before serving, place the plate under the broiler (or in a preheated 500 degree F oven). The outer skin of the meringue will turn brown, while maintaining a soft core. The ice cream will remain frozen underneath.
Place the egg whites and sugar in a large metal mixer bowl set over simmering water. Whisk constantly until the sugar melts and the mixture is very thin and warm. Remove the bowl from the heat and whisk on high speed until stiff peaks form, about 5 minutes. Continue beating on low speed until cool, about 15 more minutes.