In a small mixing bowl sift the cornstarch, flour, and salt together.
In a separate mixing bowl cream the butter and ½ cup confectioners' sugar together on medium speed 2 - 3 minutes.
Beat in the vanilla. Scrape down the sides of the bowl.
Slowly add the dry ingredients on low speed and beat until the dough comes together. Knead it together a few times right in the bowl.
Line 2 large baking sheets with parchment paper.
Scoop up slightly rounded teaspoons of dough and roll into a ball. Place on the baking sheet 2 inches apart. Refrigerate 20 minutes.
Preheat the oven to 375 degrees F.
Bake the cookies 11 - 12 minutes until golden around the edges. Cool 10 minutes on baking sheet.
Sprinkle confectioners' sugar generously over the top of the cookies while still warm. Let cool completely.
When they're completely cooled sprinkle the tops again with more confectioners' sugar.
Store tightly covered in a cool, dry place up to 1 week.