Preheat oven to 350 degrees F. Line a large baking sheet with parchment paper and set aside.

In a medium bowl, whisk together the flour, cornstarch, baking soda, salt, and baking powder. Set aside.

In the bowl of a stand mixer fitted with the paddle attachment, beat the butter on medium speed for 1 minute. Add 1 3/4 cups of the sugar and beat until light and fluffy, about 2 minutes. Stop and scrape down the sides of the bowl with a spatula, as necessary.

Add the egg, egg yolk, vanilla extract and mix until well combined.

With the mixer off, add the dry ingredients. Mix on low until just combined.

Stir in the mini chocolate chips with a spatula. Don’t over mix.

Put the 1/3 cup of sugar in a small bowl. Form the dough into balls, about 2 tablespoons per cookie. Roll each ball in the sugar until well coated. Place on the prepared baking sheet, about 2 inches apart.

Gently press extra mini chocolate chips on top of the cookie dough balls.

Bake for 10 to 12 minutes or until the cookies start to crack. They will be soft in the centers and slightly set around the edges. Check early, every oven is different. Don’t over bake or the cookies won’t be soft and chewy.

Remove the pan from the oven and sprinkle with flaky sea salt, if using. Let the cookies cool on the baking sheet for 5 minutes. Transfer the cookies to a cooling rack and cool completely.