In the top of a double boiler, mix sugar, cornstarch, and salt. Stir in orange and lemon juices and slightly beaten egg yolks. Cook over hot water until thick, 30-60 minutes.
Beat egg whites until stiff, not dry. Fold into pudding mixture while hot. Cut cake into four layers. Spread layers with hot mixture liberally. Ice the whole cake with any leftovers. Refrigerate overnight.
Several hours before serving, whip cream and sweeten. Ice cake with cream and decorate with orange slices, patted dry. Serves 8-10 people.
