MELT chocolate and butter over hot, not boiling water, stirring often. Beat egg yolks with hot coffee and icing sugar until light and fluffy. Beat egg whites until just stiff. (Do not overbeat). Stir melted chocolate into the yolk mixture and then fold in egg whites. Pour over crust and freeze until firm (about 2 hours). Spoon ice cream over chocolate layer and spread into an even layer. Freeze until firm and unmold.