Preheat oven to 375°F and line a baking sheet with parchment paper and set aside. It is best if you use two baking sheets and rotate them for the batches. Dropping the second batch of dough on the hot cookie sheet will slightly change the structure of the cookie.
Pull the butter out of the refrigerator to sit at room temperature 15 minutes before using.
14 tablespoon unsalted butter
In a medium bowl, whisk together the flour, cocoa, salt, baking soda, and espresso powder, and set aside.
1¾ cup all-purpose flour, ⅓ cup Dutch cocoa powder, 1 teaspoon salt, ½ teaspoon baking soda, ½ teaspoon espresso powder
Add 10 tablespoons of butter to a skillet and cook over medium heat until melted. Continue cooking and stirring frequently for 2 to 3 minutes until brown bits start to form in the bottom of the pan, the top is foamy, and it has a nutty aroma. Remove from heat and stir in the remaining 4 tablespoons of butter until melted. Pour the butter into a stand mixer bowl fitted with a whisk attachment.
Add the dark brown sugar, granulated sugar, and vanilla to the butter and mix to combine.
¾ cup dark brown sugar, 2 teaspoons vanilla extract, ½ cup granulated sugar
Add the egg and additional egg yolk and mix for 30 seconds. Let rest for 3 minutes, then whisk again for 30 seconds. Repeat the resting and whisking for 2 more rounds. The batter should be smooth, thick, and shiny when done - almost like caramel sauce.
1 large egg, 1 large egg yolk
Use a rubber spatula or paddle attachment to mix the dry ingredients into the wet ingredients for 1 minute. The dough will seem very soft, this is normal and you do not need to chill it.
Fold in the chocolate chips with a rubber spatula. Use your hands if necessary to make sure all of the chips are thoroughly mixed into the dough without mixing too hard.
⅔ cup dark chocolate chips, ⅔ cup milk chocolate chips, ⅔ cup white chocolate chips
Portion the dough out with a large cookie scoop and drop the scoops of dough 3-inches apart on the prepared baking sheet. Gently press the dough down to flatten the cookies. Top the dough with additional chocolate chips if desired for a more finished look. I prefer to add the extra white chocolate chips on right after they come out of the oven so they don't brown.
Bake for 8 to 10 minutes, rotating halfway through. Remove from the oven and allow the cookies to cool for 3 minutes on the baking sheet before transferring them to a wire rack.