1 (6 oz.) pkg. semi-sweet chocolate chips (1 c.)
1/2 c. sugar
1 1/4 c. graham cracker crumbs
2 tbsp. sugar
1/4 c. butter, melted
2 (8 oz.) pkg. cream cheese, softened
3/4 c. sugar
1/2 c. sour cream
1 tsp. vanilla extract
4 eggs

Combine chocolate chips and 1/2 cup sugar over hot water; heat until chocolate melts and mixture is smooth. Remove from heat; set aside. In small bowl, mix graham cracker crumbs, 2 tablespoons sugar, and melted butter. Pat firmly into bottom and 1 1/2 inch up sides of 9 inch springform pan. In a large bowl, beat cream cheese until light and fluffy. Gradually beat in 3/4 cup sugar. Mix in sour cream and vanilla. Add eggs, oven at a time, beating well. Divide batter in half. Stir melted chocolate mixture into one of the halves; pour into pan. Gently pour in remaining half. Drag a knife through batter, swirling plain batter with chocolate batter to marbelize. Bake at 325 degrees or 50 minutes, until only 3-4 inch circle in center shakes. Cool at room temperature; refrigerate until ready to serve.