Cream butter and sugar till smooth. Stir in flour and cornstarch till well combined.
Cover or wrap in plastic wrap and chill for at least 30 minutes.
Roll into 1" balls and place on ungreased cookie sheets. Bake at 325° for about 15-18 minutes.
Cool completely on cooling racks, then frost with lemon cream cheese frosting.
For frosting: Beat butter, cream cheese, and salt till smooth and creamy. Add lemon zest and enough powdered sugar to make a spreadable frosting. Frost the tops of the cookies.
Notes
These cookies work best if you let the butter soften at room temperature on the counter instead of in the microwave.
Make sure you use an ungreased cookie sheet for best results.