Combine sugar, cornstarch, salt, and water in a medium saucepan. Stir until dry ingredients dissolve. Cook over low heat, stirring constantly, 5 minutes or until mixture is clear. Add butter, orange rind and juice; stir well. Continue to cook, stirring constantly, 5 minutes or until sauce thickens.
Spoon sauce into hot sterilized jars. Cover with metal lids, and screw bands tight. Serve warm over steamed puddings or plain cakes. Store in refrigerator.