Whisk sugar and yolks in medium bowl until thick. Bring cream to boil in heavy medium saucepan. Gradually whisk hot cream into yolk mixture. Return mixture to same saucepan and stir over medium-low heat until custard thickens and coats spoon, about 3 minutes (do not boil). Remove from heat. Add chocolate to hot custard; stir until melted and smooth. Mix in amaretto. Cover and freeze until firm enough to shape, at least 3 hours and up to 24 hours.
Using 1 tablespoonful mixture per truffle, shape mixture into rounds; roll some rounds in almonds and some in chocolate. Arrange in single layer in waxed paper-lined container. Freeze up to 1 month. Serve frozen.
