it with the tube. fold the top of the bag back to form a cuff and hold it in one hand. (or, place the bag in a tall glass and fold the top back to form a cuff.) using a rubber spatula, scoop the icing into the bag. unfold the cuff and twist the top of the bag closed. squeeze the icing down to fill the tube. always practice first on a sheet of wax paper or aluminum foil to check the flow and consistency of the icing. traditional royal icing: substitute 3 large egg whites for the powder and water. 