Melt butter in a saucepan over medium heat. The butter will begin to foam. Whisk butter regularly as it cooks.
After a couple of minutes, the butter will begin to brown on the bottom of the saucepan. Continue to whisk, and remove from heat as soon as the butter begins to turn amber brown and smells rich and nutty.
Stir in brown sugar.
Set aside to cool for 5-10 minutes or until cool enough to touch.
Whisk in egg, egg yolk, and vanilla until combined.
Add the dry ingredients, and stir in until just combined.
Stir in the chocolate chips.
Cover, and chill dough for at least 1 hour.
Once dough is chilled, preheat the oven to 375 F. Line two cookie sheets with parchment paper or silicone baking mats.
If the dough has been in the fridge for longer and has gotten really hard, take dough out to sit while you preheat the oven.
Scoop out 1.5 tablespoons dough (medium cookie scoop), and place 2 inches apart on prepared baking sheet.
Bake 6-11 minutes, or until the edges of the cookies are golden brown. The centers should still look underdone.
Let the cookies cool on the sheets for 5 minutes.
Sprinkle lightly with coarse sea salt, if using, and remove to wire cooling rack to finish cooling.
Butter: I use salted butter in this recipe. You can use unsalted butter and adjust the amount of salt to taste.
Brown sugar: I use light brown sugar, but you could use dark brown sugar. Dark brown sugar will give the cookies more caramel flavor.
Flour: It's important to properly measure the flour. To measure the flour, either weigh the flour or sift/stir to aerate. Then lightly spoon into a measuring cup and level.
Kosher salt: You can substitute ¼ teaspoon of table salt in place of the kosher salt.
Chocolate chips: Feel free to use another type of chocolate chip, like dark or milk, in place of the chocolate chips.
Mixing: I like to mix these cookies by hand to avoid over-working the dough.