Step 1: Take the first half of the butter and melt it. Then, add the milk powder and brown all of the milk solids. (This is in order to increase the nutty flavors without browning all of the butter and altering the texture too much.) Put aside to cool.
Step 2: Add the cooled browned butter mixture plus unbrowned butter to the sugars in one of the two bowls. Whisk and take minute-long breaks until the mixture becomes glossy. (This is for the sake of dissolving some sugar so that they become a little crispy.)
Step 3: Add the egg and yolk and mix again.
Step 4: Combine the dry ingredients.
Step 5: Toss the chocolate chips with the combined dry ingredients, then add the dry ingredients plus chocolate into the wet ingredients.
Step 6: Mix until just combined.
Step 7: Refrigerate cookie dough at least overnight. This helps the flavors develop and allows the dissolved sugar to recrystalize, improving texture.
Step 8: Remove the cookie dough from the refrigerator and form into as big of dough balls as you'd like your cookies to be.
Step 9: Bake at 350 degrees Fahrenheit for 8-11 minutes.
Step 10: Remove from the oven, allow to cool, and enjoy!