Preheat oven to 350 F. In a large bowl using either a hand or a stand mixer, beat softened butter and powdered sugar together until fluffy.
Add in flour, cornstarch and salt, beat until all of the flour is incorporated. Add in milk, beat until a thick dough forms.
Either roll dough out onto a floured surface and cut out cookies with a cookie cutter. Or roll dough into balls and place onto ungreased baking sheets. Bake for 10-12 minutes.