First brown the butter. Follow the instructions in this post here to learn how to brown butter. It’s easy! Brown specks and a dense golden foam will form at the surface when it is nearly ready. Pour it out into a clean bowl and let it cool for 10 minutes. This whole process takes around 8-10 minutes. Immediately pour it into a large mixing bowl, then let it cool for 20-30 minutes until it reaches a temperature just warmer than room temperature. If you care to measure, the butter should read 34°C or 93°F on a thermometer. It should not be hot, but it should not be too cool or it will stiffen up when you mix in the other ingredients if it is cold in your kitchen.

Combine flour, baking soda and salt in a medium bowl and whisk well to blend evenly.

Combine cooled brown butter with both sugars in a large bowl and mix gently to combine. It should look thick like wet sand. You can also mix it in the bowl of a stand mixer fitted with the paddle attachment and beat on medium speed for 20 seconds.

Add the egg, milk and vanilla and mix it in until well incorporated and creamy-looking. Do not beat vigorously at this stage because if it is cold in your house, the butterfat will firm up and become stiff.

Add flour mixture and fold it in or mix on low just until mostly combined, then add the chocolate chunks before all of the flour is incorporated and continue mixing until they are evenly distributed. Cover the bowl and refrigerate the dough for 1-2 hours.

Preheat your oven to 375°F and line two large cookie sheets with parchment paper.

Use a 1 ½-oz cookie scoop to portion dough into 15 pieces and roll into smooth balls. Place them onto prepared baking sheets, spacing them 3 inches apart. Do not flatten. Bake for 8-10 minutes until golden on top, browned around the edges and soft in the middle. If you prefer thinner cookies, bake at 350°F for 9-11 minutes, and if you prefer smaller cookies you can roll into 18 balls and bake at 350°F for 8-10 minutes.

Let cookies cool on baking sheet for 2 minutes before carefully transferring to a wire rack to finish cooling.