Crust: Mix crumbs and butter; press onto bottom of 9-inch springform pan. Bake at 325 degrees F for 10 minutes.
Filling: Beat cream cheese, sugar and vanilla extract with electric mixer until well blended. Add chocolate, liqueur, and eggs; mix just until blended. Pour over crust.
Bake at 325 degrees F for 55 to 60 minutes or until center is almost set if using silver springform pan. Bake at 300 degrees F for 60 to 65 minutes or until center is almost set if using a dark nonstick springform pan. Run knife around rim of pan to loosen cake; cool before removing rim of pan. Refrigerate 4 hours or overnight.