Preheat oven to 350 degrees F. Line baking sheet with parchment.

Beat butter and sugars till creamy. Add egg and vanilla.

Add flour, cornstarch, baking soda and salt. Fold in chocolate. Chill dough at least an hour (speed it up in freezer if you want)

Using a cookie scoop drop dough onto sheet. Mine baked about 14 minutes but check the time depending on the size. They should be lightly brown. The tops do not really brown so don’t over bake.