In a large bowl using a hand mixer or a stand mixer fitted with a whisk attachment, beat all of the icing ingredients together on high speed for 5 minutes. When lifting the whisk up off the icing, the icing should drizzle down and smooth out within 10-15 seconds. If it’s too thick, add a little more water. If it’s too thin, add a little more sifted confectioners’ sugar.
Icing completely dries in about 2 hours at room temperature. If you’re layering royal icing onto cookies for specific designs and need it to set quickly, place cookies in the refrigerator to help speed it up.