1. Heat oven to 350°F. Grease and flour 8-inch round pan. Stir together cake mix and sugar in medium bowl; add 1/3 cup water, melted chocolate and egg, beating until blended. Add oil and remaining 1/4 cup water; beat until smooth and well blended. Pour batter into prepared pan. Bake 15 to 20 minutes or until wooden pick inserted in center comes out clean. Cool 10 minutes; remove from pan to wire rack. Cool completely. Cover; freeze until firm.
2. Meanwhile, line 2-1/2 quart dome-shaped bowl with foil. Soften ice cream and pack evenly into prepared bowl. Cover; freeze until firm.
3. Prepare MERINGUE. Heat oven to 450°F. Cover wooden board or cookie sheet with foil. Center frozen cake layer on foil; invert and unmold ice cream onto top. Peel off foil from ice cream. Spread meringue evenly over entire surface, covering holes and sealing edges down to foil. Bake 3 to 5 minutes or just until lightly browned. Remove from oven; serve immediately. Or, cover with cake saver lid (not foil or plastic wrap) and immediately return to freezer; serve frozen. 10 to 12 servings.
MERINGUE: Stir together 1/2 cup cold water, 1 tablespoon meringue powder and 1/4 cup sugar in large bowl. Beat 5 minutes until blended; gradually add additional 1/4 cup sugar, beating until meringue is stiff and dry. Use immediately.