You only need two ingredients for a nice lemon glaze: Icing sugar and lemon juice. Don't worry if it seems like there's not enough lemon juice at first, the icing sugar will quickly absorb it all. If you add too much juice, your glaze won't be as nicely white and thick! The glaze also firms up and whitens as it hardens, which is why I recommend glazing at least 10 minutes before serving, and waiting for the cake to cool completely before drizzling it with the glaze. If you like your glaze EXTRA thick, wait for it to fully firm up. Then, add another layer of glaze on top of the glaze.