Preheat oven to 325°F. Place parchment paper on 2 cookie sheets.
Cream the butter in a large bowl with an electric mixer until smooth. Set aside.
Whisk the flour, powdered sugar, cornstarch, and salt together in a small or medium bowl.
Pour about half of the flour mixture into the large bowl with the butter and vanilla extract, and mix until combined.
Add the remaining dry ingredients and continue mixing at medium speed until the cookie dough is thick and fluffy, at least 2 minutes.
Use a medium cookie scoop (1 ½ tablespoons) to scoop out cookie dough and roll it into a tight ball between your palms.
Place the cookie dough on the parchment-lined cookie sheets, about 2 inches apart.
Press the back of a fork into the top of each cookie. Dip the fork in extra flour so it won't stick to the cookies.
Top each cookie with sprinkles, if desired.
Bake the cookies, one cookie sheet at a time, for 15 minutes or until they have puffed up and the tops are dry.
Let the cookies cool completely on the cookie sheets before serving.
