Combine the butter and sugar in a large mixing bowl. Mix on medium speed for 2 minutes. Add the egg yolks, vanilla, lemon zest, lemon juice and salt. Then slowly mix in flour. Mix just until combined.
Wrap the dough in plastic wrap and refrigerate for 1 hour.
Preheat the oven to 350°F. Line a baking sheet with a silicone mat or parchment paper. Roll the cookie dough into 1 1/2 inch balls. Then press down with a cup. Bake for 10-13 minutes, or until the bottoms are lightly golden. Transfer the cookies to a cooling rack.
To make the lemon icing for cookies, whisk together the powdered sugar, lemon zest and lemon juice in a medium size bowl. Add a teaspoon of water at a time, until you reach a nice and smooth glaze. Then drizzle or spoon on top of the cookies. Allow the glaze to set before serving. Enjoy!
Slighted adapted from The Cookies and Cups Cookbook