Espresso Chocolate Cheesecake

For Crust:

Preheat oven to 325 degrees. Butter a 9 inch springform pan. Stir together cookie crumbs and butter in a medium bowl until evenly moistened. Press into bottom and 1 inch up sides of prepared pan. Bake crust 10 minutes. Cool on a rack. Wrap outside of pan tightly with foil.

For Filling:

Beat eggs with sugar in a large bowl until light and fluffy. Add cream cheese and beat until smooth. Add cornstarch, 1 tsp. vanilla and sour cream. Beat until smooth. Transfer 2 cups filling to a small bowl. Add melted chocolate to filling in large bowl and stir to blend. Beat cream to soft peaks in a small bowl. Fold whipped cream into chocolate mixture. Stir together espresso powder and 1 tbsp. vanilla in a small bowl. Stir espresso mixture into filling in small bowl. Pour chocolate filling over prepared crust. Spoon espresso mixture gently over chocolate filling, being careful not to blend the layers. Place cheesecake into a large roasting pan. Add enough hot water to come 2 inches up sides of springform pan. Bake cheesecake 90 minutes. Turn oven off and let cheesecake sit 15 minutes. Remove cheesecake from oven and cool to room temperature on a rack. Cover and refrigerate overnight. Remove pan sides to serve. Garnish with whipped cream and chocolate curls if desired.