PREPARE and bake cake mix according to package directions for 13 x 9-inch cake. Cool slightly. Turn out on sheet of aluminum foil. Cool thoroughly; set aside.
LINE 13 x 9-inch baking pan with foil. Stir together sweetened condensed milk, chocolate syrup and 1 cup chopped almonds, if desired, in large bowl. Fold in whipped cream. Pour into prepared pan; cover.
FREEZE 6 hours or until firm. Lift ice cream out of pan with foil; turn out evenly on top of cake layer. Quickly frost top and sides with whipped topping. Drizzle with chocolate syrup. Garnish with additional almonds if desired. Return to freezer at least 2 hours before serving.
Can be made 2 weeks ahead.
*To toast nuts: Place nuts in dry nonstick skillet; cook over medium heat, shaking pan until nuts are lightly browned.