PREHEAT oven to 350°F if using a silver 9-inch springform pan (or 325°F if using a dark 9-inch nonstick springform pan). Mix cookie crumbs and 2 tablespoons butter; press firmly onto bottom of pan. Set aside.
BEAT cream cheese and sugar in large bowl with electric mixer on medium speed until well blended. Add pumpkin and pumpkin pie spice; mix well. Add eggs, one at a time, mixing on low speed after each addition just until blended. Pour over crust.
BAKE 50 to 55 minute or until center is almost set; cool slightly. Carefully spread sour cream over top of cheesecake. Run knife or metal spatula around rim of pan to loosen cake; cool before removing rim of pan.
PLACE chocolate and 1 teaspoons butter in small microwaveable bowl. Microwave on MEDIUM (50%) 30 sec.; stir until chocolate is completely melted. Drizzle over cheesecake in spiral pattern. Starting at center of cheesecake, pull a toothpick through lines from center of cheesecake to outside edge of cheesecake to resemble a spider's web. Refrigerate 4 hours or overnight. Store leftover cheesecake in refrigerator.