Place the egg yolks in the top part of a double boiler and beat over barely simmering water until they are lemon-colored.
Gradually add the sugar and continue beating until fluffy. Stir in the cornstarch, the liqueur, orange rind and juice. Continue to cook and beat until the mixture has the consistency of mayonnaise. Do not allow the sauce to boil or it will curdle.
Beat the egg whites until stiff and fold them gently but thoroughly into the orange mixture. Pour into aglass serving bowl and refrigerate until well chilled.