Pre-heat the oven to 390F and line two large cookie sheets with baking parchment.
By hand, beat together the butter and powdered sugar until smooth, followed by the vanilla.
Gradually stir in the flour until you have an even dough, but try not to over mix.
Roll the cookie dough into 1 1/2 inch balls and transfer to them to the cookie sheet. Don’t worry about keeping any more than 1 inch space between them on the sheet as they barely spread in the oven.
Bake the first tray for 10-12 minutes, until the cookies are set and only just have the hint of color. Meanwhile, add about 1/2 cup more icing sugar to a shallow dish.
As soon as the cookies are cool enough to touch, roll them in the powdered sugar and transfer them to a wire rack to cool. Meanwhile, bake the second tray and repeat.
Once the cookies are completely cool, roll them in the powdered sugar again for a second coating.