Mix chocolate cake batter according to the box directions, but add 1 extra cup of water (the batter should have the consistency of chocolate syrup). Ladle the batter into a round nonstick pan preheated with butter, swirling the pan in a circular motion as soon as the batter hits it to form a thin shell. Flip when cooked on one side. Top half of the shell with whipped cream, sliced bananas, broken nut brittle and caramel sauce, then fold the other half over to cover. Dust with confectioners sugar.