Preheat oven to 350F.
In a small bowl, soak cranberries in Calvados (or cider) until softened, about 10 minutes.
Use 2 teaspoons butter to thickly coat bottom and lightly coat sides of a 9-inch spaure or 7-by-11-inch baking pan. Spread ½ cup brown sugar evenly in bottoom of pan. Make 3 rows of apple slices over sugar, overlapping them slightly. Sprinkle with reserved cranberries. Set aside.
Melt remaining 4 teaspoons butter. Set aside.
In a food processor, finely grind Zwieback. Add flour and salt and process until well combined.
In a Large mixing bowl, combine eggs, egg whites, vanilla and remaining ½ cup brown sugar. Beat with an electric mixer on high speed until thick and pale, about 5 minutes. With mixer at low speed, add reserved Zwieback mixture and melted butter, beating until just combined. (Do not overmix.) Spoon over fruit in prepared pan.
Bake cake for 30 for 35 minutes, or until top is golden and springs back when touched lightly. Transfer pan to a wire rack and let cool for 5 minutes. Invert cake onto a wire rack and let cool completely.