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

In another bowl, beat together the butter and sugars until creamy and lighter in color, about 3-4 minutes. Add the egg and yolk, beating until well combined. Beat in the vanilla extract.

Add the dry ingredients to the butter and sugar mixture. Beat on low speed until combined. Stir in the chocolate chunks.

Scoop ½ cupfulls of dough onto baking sheets lined with silicone mats or parchment paper. Cover with saran wrap and chill for at least two hours. Alternatively, you can chill the dough before scooping. I just find it’s easier to scoop dough before it’s chilled.

Bake at 350 degrees (4 cookies per pan) for 13-15 minutes or until the cookies are starting to brown on the edges, but still light in color and just barely gooey in the center. Press extra chocolate chips or chunks into the tops of the cookies, if desired. Sprinkle with sea salt. Allow to set up on the pan for 5-10 minutes, then transfer to a wire rack to cool completely.