Add the butter to a saucepan over medium heat and let it start to simmer, then reduce the heat to medium-low.
1 cup unsalted butter
Whisk the entire time as a foam starts to form at the top of the butter and continue whisking until the butter starts to turn a light brown color and become fragrant.
Remove the pan from the heat and pour the butter into a large heatproof bowl to cool completely for about 30 minutes.
Whisk in the brown sugar, granulated sugar, eggs, and vanilla. Set aside.
¾ cup brown sugar, ½ cup granulated sugar, 2 large eggs, 2 teaspoons pure vanilla extract
In a separate large bowl, whisk the flour, cornstarch, baking soda, baking powder, and salt together. Stir into the wet ingredients until completely combined.
2⅔ cups all-purpose flour, 2 teaspoons cornstarch, 1 teaspoon baking soda, ½ teaspoon baking powder, ½ teaspoon kosher salt
Stir in the milk chocolate chips and semisweet chocolate chips, then cover the bowl with plastic wrap and refrigerate for 1 hour.
1 cup milk chocolate chips, 1 cup semisweet chocolate chips
Preheat oven to 350°F and line a baking sheet with parchment paper.
Form six 1-inch balls from the cookie dough and place them spread evenly apart on the prepared baking sheet.
Lightly press down on the tops of the cookies, press in a few extra chocolate chips on top, and bake for 8-10 minutes, or until the edges of the cookies start to dry out and turn a light golden color.
Let cool completely on the pan, then remove them from the pan and set aside.
Repeat the baking process with the remaining cookie dough, then serve.