Line an (8 1/2 by 4 1/2 by 2 1/2-inch) metal loaf pan with 2 layers of plastic wrap, allowing 3 inches of plastic to hang over pan sides. Cut ice cream block in half crosswise, and then press the layer of pound cake slices into the bottom of the pan. Add half of ice cream and then add the remaining cake to sandwich the ice cream. Fold plastic overhang atop cake to cover. Freeze for 4 hours, or until frozen solid.
Wrap hot damp towels around pan sides to loosen cake and ice cream from pan. Fold back plastic from atop cake. Invert a baking dish or large flame-proof plate atop cake. Holding baking dish and pan together, invert cake into dish. Remove pan; keep cake covered with plastic wrap. Freeze while preparing meringue.
Preheat oven to 450 degrees F.
Beat egg whites in the bowl of an electric mixer until frothy. Add cream of tartar and continue beating until soft peaks form. Gradually add sugar and beat until stiff peaks form. Remove plastic from cake. Spread meringue over cake, covering cake and ice cream and completely sealing meringue to dish. Bake until meringue is lightly brown and just set, about 3 minutes. Cut into slices and serve immediately.