- Make crust: Preheat oven to 350 degrees Fahrenheit. Wrap outside of 9-inch diameter springform pan with 2 3/4-inch-high sides with double thickness of foil. Spray bottom of pan with vegetable oil spray. Finely grind cookies in processor. Add butter and process until blended. Press mixture onto bottom (not sides) of prepared pan. Refrigerate while preparing filling.
- Make filling: Combine cream and coffee powder in medium saucepan. Stir over medium heat until coffee powder dissolves. Reduce heat to low. Add chocolate; whisk until chocolate melts and mixture is smooth. Cool 10 minutes.
- Using electric mixer, beat cream cheese and sugar in large bowl until well blended. Beat in cornstarch. Add sour cream and vanilla; beat well. Add eggs one at a time, beating just until blended after each addition. Whisk one cup cheese mixture into chocolate mixture. Return chocolate mixture to remaining cheese mixture; whisk until smooth.
- Pour batter into crust. Place springform pan in large baking pan. Add enough hot water to baking pan to come halfway up sides of springform pan. Bake cheesecake until softly set and slightly puffed around edges, about 1 hour. Turn off oven. Let cake stand in oven 45 minutes. Transfer springform pan to rack and cool. Cover; chill cake overnight.
- Make glaze: bring cream to boil in heavy small saucepan. Remove from heat. Add 4 ounces chocolate and whisk until melted and smooth. Pour glaze over top of cake. Using spatula, smooth glaze evenly over top. Refrigerate until glaze is set, at least 2 hours. (Can be prepared 1 day ahead. Cover and refrigerate.).
- Using knife, cut around sides of pan to loosen cake. Remove pan sides. Cut into wedges and serve.