Cut a piece of cardboard the size of the cake. Wrap in aluminum foil. Set aside. Line the loaf pan with plastic wrap so it hangs well out over the edge. (The plastic wrap will be used to help lift the ice cream and cake loaf from the pan when it comes time to frost with meringue, bake and serve.)
Spoon the ice cream into the loaf pan. Scatter the dry cherries or candied fruit, if you are using, as you layer the ice cream into the loaf pan. Press down on the ice cream to make it as even as possible. Fill the pan about 3/4 full or to within 1-inch of the top edge of the loaf pan. Place one slice of cake on the ice cream. Place the cardboard on top. Bring the pieces of plastic wrap up over the top of the ice cream loaf to cover, then place in the freezer. The Baked Alaska may be prepared up to two weeks ahead to this point and stored in the freezer before serving.
About 30 minutes before you plan to serve the dessert, place the ice cream loaf in the refrigerator to temper slightly if it is very firm. Turn on your broiler.
Place the egg whites and sugar in the bowl of an electric mixer. Whisk to combine. Place the bowl over a pan of simmering water. Whisk gently until sugar dissolves completely (there should be no gritty feeling when you rub some of the mixture between your thumb and index finger), and the egg whites are uniformly hot (about 130 degrees).
Remove the bowl from the pan and return to the electric mixer. Whip on medium speed until the meringue is cool and increased in volume. It should be stiff but not dry and lumpy.
Unmold the ice cream loaf onto an oven proof serving platter. Top the loaf with another slice of the cake. Frost the cake with the meringue about 1-inch thick. Seal the ice cream loaf completely with meringue. Use a pastry bag fitted with a star tip to pipe additional meringue along the edges for a decorative effect.
Immediately place the cake in the oven. Watch the meringue very closely. As it browns, move the pan so that it colors evenly. It should bake no more than 5 or 6 minutes.