Mix sugar and flour with beaten eggs yolks. Add scalded milk slowly. Then add butter and salt and cook over hot water until thickened. Add orange rind and juice. Cool slightly and fold in stiffly beaten egg whites.
Split ladyfingers and place a layer in a pan lined with wax paper. Spread with orange mixture. Cover with another layer of ladyfingers and continue until mixture is used.
Chill overnight. Serve with sweetened whipped cream.