Preheat the oven to 350F, then line a baking sheet with parchment paper or silpat.
In a medium bowl, cream the butter and both sugars together. I did so using my spatula.
4 tablespoon butter, ¼ cup brown sugar, 2 tablespoon granulated sugar
Add in the vanilla and egg yolk and mix everything is smooth and well incorporated.
1 yolk, 1 teaspoon vanilla extract
Add in the dry ingredients over the wet ingredient mixture, starting with the flour, corn starch, baking soda, and salt. Stir just until combined.
⅔ cup flour, 1 tablespoon corn starch, ¼ teaspoon baking soda, ¼ teaspoon salt
Fold in the chocolate chips, then using a medium cookie scoop, scoop out the cookie dough into 8 2-tablespoon cookie dough balls and place on the prepared baking sheet. ( READ NOTES FOR LARGER COOKIES)
½ cup semi sweet chocolate chips
Place them on the prepared baking sheet and bake for 8 minutes. Don't worry if they look underdone or gooey in the middle. That's what we want, they will continue to bake even after you pull them out of the oven to cool.
Top the cookies with extra chocolate chips as soon as they come out of the oven, cool on the cookie sheet for 5 minutes then transfer to a cooling rack.