In the bowl of a stand mixer, add melted butter and sugars. Stir until well combined.

Add in the egg and egg yolk, stir well. Stir in vanilla extract.

In a medium-sized bowl, whisk  flour, cornstarch, baking soda, and salt together.

Gradually add flour mixture to the  stand mixer. Mix well so that all the flour is absorbed. Stir in chocolate chips.

Place dough in refrigerator and chill for 30 minutes.

Preheat oven to 350 dergrees and prepare cookie sheets by lining with parchment paper.

Scoop dough into 1 ½ tablespoon rounds and place onto prepared cookie sheets, placing at least 2" apart.

Bake at 350 degreea for 11 minutes. Cookies may still look slightly soft in the centers, that is OK, they will cook completely on the cookie sheets. Don't over-bake or your cookies will be too hard.

Allow to cool completely on cookie sheets. Makes 30 cookies