Prepare the icing by mixing together icing sugar and enough lemon juice to make a thick, almost viscous icing. Make sure your icing sugar is sifted and has no lumps. Spoon the icing into a piping bag. Snip off a very small part of the tip and decorate the cookies as desired. Remember that this icing isnu2019t as hard as regular Royal icing, so if youu2019re planning to pack and mail them, you will need to be very careful.