1Crust-In a medium bowl, mix together chocolate crumbs and melted butter until blended. Press into a 9 inch springform pan. Preheat oven to 300.
2Filling-In a large bowl, beat together cream cheese, sugar, and eggs at medium speed until smooth and fluffy. Spoon half of cream cheese mixture into crust.
3Stir the melted 2oz (2 squares) in the remaining cream cheese mixture until well blended. Drizzle over batter in crust to make swirls.
4Bake cheesecake 50 minutes or until cheesecake tests done. Transfer pan to a wire rack. Cool completely. Transfer cheesecake to a serving plate, cover with plastic wrap, and chill for 2 hours.
5Uncover cheesecake; carefully remove the side of pan. Frosting- in a small bowl, mix together the 6oz. (6 squares) melted chocolate and sour cream. spread over cheesecake. Chill until frosting is set.