Beat 1 cup unsalted butter until light and fluffy.
Add 1 teaspoon vanilla extract and ⅓ cup powdered sugar and beat until well mixed.
In a small bowl, whisk together 1 cup all purpose flour, ¾ cup cornstarch, 1½ teaspoons baking powder and ½ teaspoon salt until there are no lumps.
Mix dry ingredients into butter mixture until thoroughly combined.
If the mixture feels soft, chill for at least a half hour. Otherwise, go ahead and proceed to baking.
Roll dough into 1″ balls (I like to use my small cookie scoop to portion the dough.)
Place on ungreased cookie sheet and flatten slightly.
Bake for about 12 minutes, or until lightly golden brown.
Cool on cookie sheet for 2 minutes, then remove to wire rack to cool completely.
To glaze: mix together 1 cup powdered sugar, and ¼ teaspoon vanilla extract. Add 2 Tablespoons milk or cream a little bit at a time until you form a thick glaze consistency. Spoon a small amount onto each cookie and top with sprinkles if desired.