Step 1

In a medium bowl, mix the flour, baking soda, salt, and cornstarch with a fork to incorporate the ingredients. Set aside.

Step 2

To the bowl of a stand mixer fitted with the paddle attachment, add butter, both sugars, and vanilla. Beat on medium speed until the mix looks light and fluffy, about 2 mins. Add eggs 1 at a time, and beat until incorporated.

Step 3

Reduce the mixer speed to low, and gradually add in the flour mix until it is just incorporated into the dough. Scrape down the sides of the bowl, and add both chocolate chips to the bowl. Stir the chocolate chips and any flour from the sides of the bowl into the dough by hand using a silicone spatula or wooden spoon. Place the bowl in the fridge to chill the dough for at least 2 hours or up to overnight.

Step 4

Preheat the oven to 350 degrees. Line a large cookie sheet with parchment paper. Roll dough into 2 tbsp balls, and place them on the prepared cookie sheet spaced roughly 2 inches apart. Sprinkle the top of each dough ball with a pinch of flaky sea salt. Bake for 10-12 mins until the edges just start to turn golden brown and the tops look set but still light in color. Remove from oven, and immediately smack the tray of cookies on the countertop to release any air bubbles. Transfer cookies to a cooling rack. Repeat as necessary with remaining dough, making sure the cookie sheet cools down between each batch. Serve!