1. Prepare GRAHAM CRUST. Heat oven to 375°F.
2. Beat cream cheese, 3/4 cup sugar, cocoa and 1 teaspoon vanilla in large bowl until light and fluffy. Add eggs; beat until well blended. Stir in chocolate chips. Pour into prepared crust.
3. Bake 20 minutes. Remove from oven; cool 15 minutes. Increase oven temperature to 425°F. Stir together sour cream, remaining 2 tablespoons sugar and remaining 1 teaspoon vanilla in small bowl; stir until smooth. Spread evenly over baked filling.
4. Bake 10 minutes. Remove from oven to wire rack. With knife, loosen cake from side of pan. Cool completely; remove side of pan. Refrigerate several hours before serving. Cover; refrigerate leftover cheesecake. Makes 12 servings.
GRAHAM CRUST: Stir together 1-1/2 cups graham cracker crumbs and 1/3 cup sugar; add 1/3 cup melted butter or margarine in medium bowl; mix well. Press mixture firmly onto bottom and halfway up side of 9-inch springform pan.