To make the icing: In a large bowl, add powdered sugar, egg whites, salt, and lemon juice. Beat with an electric mixer or stand mixer with paddle attachment on medium until it is white and thick. This is what you will use to pipe around the edges of the cookies using a pastry bag and plain tip. Once you have finished piping around the edges of the cookies, let it dry for about an hour. In the meantime, you can tint and thin out the icing using either another egg white or water to flood between the piped edges. You want the consistency to be that of maple syrup. I use a paste color to tint the icing, if you are using liquid tint, don’t finish thinning out the icing until you have achieved the color you want. Once you finish flooding the cookies with icing, allow to dry for 24 hours before adding any other tint – like for eyes or mouths (or else it bleeds into the white icing).