Whisk together flour, cornstarch, and salt in a medium bowl.

Set the dry ingredients aside.

Cream together butter and 1/4 cup powdered sugar until light and fluffy.

Beat in vanilla extract.

Add the flour mixture and beat until just incorporated.

Cover the dough and refrigerate for at least one hour, or until firm.

Preheat oven to 350 degrees F (177 degrees C) and place rack in the center.

Line two baking sheets with parchment paper.

Form dough into 1-inch balls and place on baking sheets, spacing 1 inch apart.

Bake for 12-14 minutes, or until edges start to brown.

Remove from oven and cool on a wire rack for 5 minutes.

Line another baking pan or tray with parchment or wax paper.

Sprinkle half of the extra powdered sugar onto the lined pan.

Place slightly cooled cookies on top of the sugar.

Sprinkle the remaining sugar over the tops of the cookies using a fine strainer or sieve (or roll the cookies in the sugar).