Line a greased 15-in. x 10-in. x 1-in. baking pan with waxed paper. Grease the paper; set aside. Prepare cake batter according to package directions; pour into prepared pan.
Bake at 350° for 23-28 minutes or until a toothpick comes out clean. Cool on a wire rack.
Invert cake and gently peel off waxed paper. Cut cake in half widthwise. Place one half on a serving platter. Spread with ice cream; top with remaining cake. Cover and freeze.
In a heavy saucepan, combine the sugar, milk and corn syrup. Bring to a boil over medium heat, stirring constantly. Cook and stir for 2 minutes. Remove from the heat; stir in chocolate until melted. Stir in vanilla. Serve warm with cake. Sprinkle with almonds. Yield: 9 servings (1-3/4 cups sauce).