Preheat oven to 375~. Grease and flour two 9" round pans. Prepare, bake, and cool cake following package directions For filling, combine hot fudge topping and coffee crysta;s in medium saucepan. Heat until coffee crystal are dissolved. Cool. Fold 2 cups whipped topping into fudge topping mixture. Refrigerate 30 minutes. Place one cake layer on serving plate. Spread with 1 cup filling. Top with second cake layer. Add remaining 2 cups whipped topping to remaining filling. Frost top and sides of cake with topping mixture. Tip: Garnish with chocolate curls, coated coffee beans, or grated chocolate.