Place all of the ingredients in the bowl of an electric mixer and beat slowly until they are all blended. Then beat at medium speed until the icing forms stiff peaks, about 5 minutes. Add more sugar if the icing is not stiff enough, or a few drops of water if it is too stiff. Use immediately or cover the bowl with a damp cloth to prevent drying when not in use. Allow at least 24 hours for royal icing decorations to dry, at room temperature.