In large bowl, beat butter until creamy with a mixer.
Add sugars and combine with mixer.
Beat in the eggs and vanilla.
In another bowl, combine flour, cornstarch, salt and baking soda.
Mix in the wet ingredients on low speed.
Cover with plastic wrap. Refrigerate for 2 hours.
Let the dough rest at room temp for 10 minutes.
Preheat your oven to 350.
Roll dough into balls and place on baking sheet.
Bake 8-10 minutes. No longer. If you want them flatter, then just press them down slightly as they cool with a spoon.
Allow to cool for 5 minutes and Enjoy!