Brown the butter: in a medium saucepan, over medium heat, melt the butter and stir constantly with a whisk (or spatula) until it starts to turn brown and give off a nutty aroma. Keep an eye on it because it can burn quickly. This takes around 5 - 7 minutes. Take off heat and let cool for 10 - 15 mins.

In a large bowl, mix your wet ingredients: start by creaming your brown butter, brown sugar, and granulated sugar (make sure to pour all the butter and brown bits off of the pan). Using a hand mixer, beat on medium speed until light and fluffy (do not overmix; you know it’s ready if you pinch the mixture between two fingers and feel little to no sugar granules). Add the egg, egg yolk, and vanilla and mix to combine.

In a medium bowl, whisk together your dry ingredients: flour, cornstarch, baking soda, and salt.

Add half of your dry ingredients into your wet mixture. Fold slowly with a spatula and then add the other half of the dry ingredients. While the dough still has some streaks of white flour, add in your chopped chocolate and chocolate chips. (They don’t have to be semi-sweet or milk, they can be anything you want). Continue folding and stop when combined.

Scoop your cookie dough into 3 - 4 oz size balls (or your preferred size) and place into a bowl or on a baking sheet. Cover in plastic wrap and chill for 24 hours, or at least 1 hour. Chilling helps the flavors of the cookie develop and prevents overspreading in the oven. If you chill them longer than an hour, let them sit 10 minutes at room temp before baking.

Preheat oven to 350 °F. Place the cookie dough balls onto two parchment paper lined baking sheets, keeping them a few inches apart. Bake for 8-11 minutes. Do not overbake the cookies, the centers will look underbaked but will continue to cook on the hot baking pan. You know they are ready once the edges and bottoms are golden brown.

Let cool for 5 minutes and transfer to a wire rack to continue cooling. Add sea salt if desired. Enjoy with cold milk!