Chocolate Swirl Cheesecake

6 oz semi-sweet chocolate chips
1/2 c sugar
1 1/4 c graham cracker crumbs
2 T sugar
1/4 c butter, melted
2 - 8 oz pkgs cream cheese, softened
3/4 c sugar
1/2 c sour cream
1 t vanilla extract
4 eggs

Preheat oven to 325. Combine over hot (not boiling) water, chocolate chips and 12/ cup sugar; heat until morsels melt and mixture is smooth. Remove from heat; set aside. In small bowl, combine graham cracker crumbs, 2 tablespoons sugar and melted butter; mix well. Pat firmly into 9" springform pan, covering bottom and 1/2" up sides; set aside. In large bowl, beat cream cheese until light and creamy. Gradually beat in 3/4 cup sugar. Mis in sour cream and vanilla extract. Add eggs, one at a time, beating well after each addition. Divide batter in half. Stir melted chocolate mixture into first half. Pour into crumb-lined pan; cover with plain butter. With a knife, swirl plain batter with cocolate batter to marbelize. Bake at 325 for 50 minutes for 50 minutes or until only 2-3" circle in center will shake. Cool at room temperature; refrigerate until ready to serve.