1 egg yolk from a large egg (discard white or save for another use)
2 tablespoons unsalted butter, very soft
2 tablespoons granulated sugar
2 tablespoons light brown sugar, packed
1/2 teaspoon vanilla extract
1/3 cup + 2 tablespoons all-purpose flour
1/2 teaspoon baking soda
1/2 teaspoon cornstarch
1/4 teaspoon kosher salt, or to taste
1/3 cup semi-sweet chocolate chips, plus more for adding on top before and after baking if desired (recommended)
Preheat oven to 350F, line a baking sheet with a Silpat or spray with cooking spray; set aside.
To a large bowl, add the egg, butter, sugars, vanilla, and mix with a spoon aggressively for about 90 seconds, or until smooth and slightly fluffed, i.e. your bicep and shoulder should be burning if you’ve mixed well enough.
Add the flour, baking soda, cornstarch (keeps cookie extra soft), salt, and stir to combine.
Add the chocolate chips and stir to combine.
Roll dough in your hands to create a ball. Place ball on prepared baking sheet and flatten about halfway or so that the mound is about 1 1/2 inches thick (because dough is not chilled, cookie will spread and flatten quite a bit while baking). If desired, add additional chocolate chips to the top of cookie (recommended)
Bake for about 12 to 14 minutes (shorter for softer cookies, longer for more well-done cookies), or until edges have set and top is just set, even if slightly undercooked, pale, and glossy in the center; don’t overbake. Cookie firms up it cools.
Remove baking sheet from oven, top cookie with additional chocolate chips as desired (recommended), and allow cookie to cool on baking sheet until serving. Cookie is best warm and fresh.