Preheat oven to 350 degrees
Beat butter until it appears creamy
Add powdered sugar and mix until light and fluffy
Add lemon zest and vanilla extract, beat well
Add flour and cornstarch and mix until well combined. The dough will slowly come together as you mix it.
Roll into approximately 1 inch balls and place on parchment lined baking sheet
Bake for 13 to 15 minutes, until bottom is light brown
Remove from oven and allow to cool for a few minutes before transferring to wire cooling rack - cookies are quite fragile and delicate when warm
Allow to cool completely before frosting
Combine all frosting ingredients, adding more or less than 1/2 cup lemon juice to get it thin enough to dip cookies
By hand, dip each cookie top side in frosting
Return to cooling rack to allow frosting to set