Zest your lemons and put the zest aside in a small bowl.
Cut lemons in half and squeeze out juice over a bowl. I like to squeeze them over a mesh strainer so I don't have to worry about the seeds. I go ahead and juice all 3, so I can make plenty of icing later.
Put the room temperature butter into the bowl of your stand mixer and let it beat the butter until it's creamy.
Add in 1/2 cup powdered sugar and mix with butter until all incorporated together.
With mixer on low, add in 2 Tablespoons lemon zest and 2 Tablespoons lemon juice.
In a separate bowl, sift flour, cornstarch and salt together and stir to combine.
Add the flour mixture in 3 or 4 additions to the butter mix. I put in a large spoonful, let it totally mix in, then put in another, and so on until all the flour mixture has been added in.
Once the dough is all mixed up, I lay out a piece of plastic wrap on the counter and empty the contents of the mixing bowl onto the wrap.
I wrap the plastic around the dough and squeeze it all together and let it form an even size log (so we can slice and bake the dough when it comes out of the fridge!).
Refrigerate for at least an hour. Overnight is totally fine also.
When it's time to bake the cookies, preheat oven to 350°.
Line a cookie/baking sheet with parchment paper or a silicone mat.
Slice the cookies off the dough log (Mine makes 24 nicely thick cookies) and place them on the parchment-lined baking sheet. Give them a little space from each other, though they will not spread a whole lot when baking.
Bake for 11-13 minutes or until lightly browned. They will not turn much in color at all, so watch your time.
Move cookies to a cooling rack to cool completely before icing.