Mix together the icing sugar, lemon zest and butter until it becomes sort of crumbly.
Remove the zest with a sharp vegetable peeler in long strips, avoiding as much of the white pith as possible.
Previous versions of this recipe have included twice the amount of frosting. In this recent update I've halved that to provide enough frosting for the middle and top as many people seem to prefer. If you want to frost the entire sides of the cake as well. please feel free to make one and a half or even two times the recipe. It depends on how much frosting is your personal preference.
The nutritional information provided is automatically calculated by third party software and is meant as a guideline only. Exact accuracy is not guaranteed. For recipes where all ingredients may not be used entirely, such as those with coatings on meats, or with sauces or dressings for example, calorie & nutritional values per serving will likely be somewhat lower than indicated.