Chocolate Lover's Cheesecake

2 pkgs. cream cheese, softened
7/8 C white sugar
1/2 C unsweetened cocoa powder
2 teaspoons vanilla extract
2 eggs
1 C semisweet chocolate chips
1 (8oz) cont. sour cream
1 1/2 C graham cracker crumbs
1/3 C white sugar
1/3 C melted butter
directions:
To make cracker crust, stir together cracker crumbs and 1/3. C sugar. Blend in melted butter or margarine. Press into bottom and 1/2way up sides of 9inch springform pan. Preheat oven to 375 degrees F.
In large mixer bowl, beat cream cheese, 3/4 C sugar, cocoa, and 1 tsp. vanilla until light and fluffy. Add eggs; blend well. Stir in choc. chips. Pour into the prepared crust.
Bake for 20 min. Remove from oven and let cool for 15 min. Increase oven temp. to 425 degrees F.
In small bowl, stir together sour cream, remaining 2 Tbs. sugar and remaining 2 tsp. vanilla. Stir until smooth. Spread evenly over baked filling. Bake 10 min. Remove from oven to wire rack. With knife, loosen cake from side of pan. Cook completely; remove side of pan. Refrigerate before serving. Cover and refrigerate leftovers-if you have any!