Combine in the top of a double boiler or a heatproof bowl placed over a saucepan or pot of barely simmering water:
Stir in:
Cook, stirring constantly, until the custard coats the back of a spoon. Pour into a medium bowl and refrigerate until cold.
Whip to soft peaks:
Fold into the coffee mixture. Divide among parfait glasses and freeze for at least 4 to 5 hours. If frozen longer, let stand at room temperature for 5 to 10 minutes before serving topped with: