Boil cream in a small heavy saucepan until reduced to 2 TBS. Remove from heat, stir in liqueur and chocolate and return to low heat. Continue stirring until chocolate melts. Whisk in the softened butter. When mixture is smooth, pour into a baking dish and refrigerate until firm (about 40-60 minutes). Scoop chocolate up with a small spoon and shape into 1 inch balls. Roll the balls in unsweetened cocoa. Place in covered container and store in refrigerator. Let truffles stand at room temperature for 30 minutes prior to serving. 24 truffles.