Directions

1. Grease bottom of 9-inch springform pan. Prepare cake batter as directed on package; pour into prepared pan. Bake at 325 degrees F for 25 minutes if using a silver springform pan. (Bake at 300 degrees F for 20 minutes if using a dark nonstick springform pan.) Cool.
2. Beat cream cheese, granulated sugar and 1 tsp. of the vanilla in large bowl with electric mixer on medium speed until well blended. Add sour cream; mix well. Add eggs, 1 at a time, mixing on low speed after each addition just until blended. Pour over cake layer in pan.
3. Bake at 325 degrees F for 40 to 45 minutes or until center is almost set if using a silver springform pan. (Bake at 300 degrees F for 40 to 45 minutes or until center is almost set if using a dark nonstick springform pan.) Run knife or metal spatula around rim of pan to loosen cake; cool before removing rim of pan.
4. Place chocolate, milk and butter in medium microwavable bowl. Microwave on HIGH 2 minutes or until butter is melted, stirring after 1 minute. Stir until chocolate is completely melted. Add powdered sugar and remaining 1 tsp. vanilla; mix well. Spread over cooled cheesecake. Refrigerate 4 hours or overnight.