Combine melted butter and sugars in a large bowl. Stir well.
Add egg and egg yolk, and mix well. Stir in vanilla extract. Set aside.
In a medium-sized bowl, whisk together flour, cornstarch, baking soda, and salt.
Gradually add flour mixture to wet ingredients. Stir well so that all the flour is absorbed. Add the chocolate chips.
Place dough in refrigerator and chill for 30 minutes.
Preheat oven to 350°F (177°C) and prepare cookie sheets by lining with parchment paper.
Scoop dough by rounded 1 ½ tablespoon onto prepared cookie sheets, placing at least 2" apart.
Bake for 11 minutes. The cookies may still seem slightly soft in the centers and that's okay. The cookies will cook completely on the cookie sheets. Don't over-bake or your cookies will be too hard.
If desired, gently press additional chocolate chips into the tops of the warm cookies.
Allow to cool completely on cookie sheets.
Notes
Recipe source:Spend with Pennies blogNOTES: Adding sea salt on top of each hot and freshly baked cookies adds a sweet and salty layer.Set aside a small amount of chocolate chips. As soon as the cookies come out of the oven, gently press extra chocolate chips on top. This gives each cookie a professional look.