Line a 9 x 5 x 2 1/2-inch metal loaf pan with plastic wrap, leaving overhang. Spoon ice cream into prepared pan, spreading evenly and smoothing top.
Cut cake horizontally in half. Arrange 1 cake piece, cut side down, atop ice cream and against one corner of pan. Cut remaining cake piece into strips and arrange in pan to cover ice cream completely. Cover with overhanging plastic and freeze until firm, at least 4 hours.
Uncover cake. Invert onto metal or other ovenproof platter. Freeze while preparing meringue. Beat egg whites in large bowl until foamy. Add cream of tartar. Beat until soft peaks form. Beat in vanilla. Gradually add sugar, beating until stiff glossy peaks form. Spread meringue over cake, covering cake completely and sealing meringue to platter. Freeze overnight.
Position rack in center of oven and preheat to 500° F for 20 minutes before using. Bake dessert until meringue is lightly browned and just set, about 3 minutes.
Cut baked Alaska into slices; arrange on plates and if desired, spoon warm sauce around dessert.Makes 6 to 8