I made the icing by first squeezing the juice out of a small lemon, then adding icing sugar until I found the consistency I wanted. I rounded it of with some vanilla extract and a bit of a water to keep the icing smooth. If you add enough water, this icing can be super smooth and you can tap the cookie to make it flatten into a smooth surface. However, this icing will not hold it's shape, so there's not much point using fancy nibs on your piping bag. As one would expect, an icing made from lemon juice has quite the tang to it. I found this works great with the sweet sugar cookie, but if you feel it might be too tangy, maybe use a tiny dash of lemon extract instead.
