Preheat oven to 350F. Stir together wafer crumbs and cinnamon. Pat into bottom of 9-inch springform pan. Beat cream cheese until light and fluffy. Beat in sugar and cocoa powder. Beat in egg. Stir in 2 cups sour cream, coffee liqueur and vanilla. Turn into prepared pan. Bake for 30 minutes or until set. Spread remaining sour cream evenly over top. Return to oven 1 minute to glaze top. Cool to room temperature, then chill thoroughly, covered. Remove from springform pan. Just before serving, dust top with cocoa powder.