Chocolate Crust: Melt butter in medium saucepan. Remove from heat. Add wafer crumbs. Mix well. Press evenly in bottom and 1 (2.5 cm) inch up side of ungreased 9 inch (22 cm) springform pan with flat-bottomed glass. Chill for 1 hour.
Coffee Filling: Sprinkle gelatin over coffee in small saucepan. Let stand for 1 minute. Heat and stir on low until dissolved completely. Cool slightly.
Beat cream cheese, sour cream, and sugar in a large bowl until smooth and well combined. Add gelatin mixture. Beat.
Beat whipping cream in small bowl until soft peaks form. Fold into cream cheese mixture. Spoon into crust. Spread evenly. Cover. Chill for at least 8 hours or overnight. Dust top of cheesecake with cocoa.
Coffee Truffles: Combine first 3 ingredients in a small heavy saucepan. Heat and stir on lowest heat, stirring often, until chocolate is almost melted. Do not overheat. Remove from heat. Stir until smooth.
Add liqueur. Stir. Turn into small bowl. Chill for about 2 hours until firm. Roll into balls using 1 tsp (5 mL) for each. Place on foil-lined baking sheets. Chill for about 1 hour until firm.
Heat melting wafers in small heavy saucepan on lowest heat for about 3 minutes, stirring often, until almost melted. Do not overheat. Remove from heat. Stir until smooth. Dip balls into white chocolate. Place, not touching, on baking sheet. Cool until chocolate is set.
Arrange truffles around outer edge of cheesecake. Dust truffles lightly with cocoa.