Cream butter and vanilla until smooth.
Add powdered sugar and salt; beat until fluffy.
Mix in flour and cornstarch just until dough comes together.
Roll into 1-inch balls and place on parchment-lined baking sheet.
Press lightly with a fork to flatten.
Bake at 325°F (160°C) for 12–15 minutes, until bottoms are just golden.
Cool 5 minutes on the pan, then transfer to a wire rack.