Cut the butter into smaller chunks so it melts evenly and place it in a light-colored saucepan. A light pan lets you see the brown bits form — they're much harder to spot in a dark pan. Set over medium heat.

Once the butter melts, whisk continuously. It will foam, especially around the edges of the pan. Keep going for about 7 to 8 minutes total.

Watch for three signs: a deeper golden color, more foam than a few minutes earlier, and a slightly different consistency where the butter starts wanting to stick to the pan. Then the foam will begin to subside and little brown flecks will form in the bottom.

As soon as those brown flecks appear, pull the pan off the heat. Butter goes from browned to burned quickly, so don't walk away from it.

Pour the brown butter into your mixing bowl and scrape the pan well with a spatula to get every brown bit. That's where all the flavor lives.

Let it cool on the counter for 10 minutes, then refrigerate for 1 hour to 90 minutes. If it firms up too much, set it out for about 10 minutes before making the dough.

Using the paddle attachment, beat the chilled brown butter for 1 to 2 minutes until it looks smooth and creamy. It will look a little funky at first — keep going.

Add the granulated sugar and brown sugar and cream together.

Add the whole egg, the extra egg yolk, and the vanilla. Mix until combined.

In a separate bowl, whisk together the flour, cornstarch, baking soda, and salt. Measure the flour by spooning it into the cup and leveling — do not pack it.

Add the dry ingredients to the dough a little at a time, starting with about a cup. Scrape down the bowl to make sure everything is incorporated.

Add the room temperature milk. Browning the butter evaporates some of its water, so this replaces that lost moisture.

Mix in most of the chocolate chips, reserving a small handful for the tops.

Scoop the dough onto lined baking sheets, about 8 per sheet to allow for spreading. Press a few of the reserved chocolate chips into the top of each cookie for a prettier finished look.

Refrigerate the scooped dough for at least 2 hours. Longer is fine. Don't skip this step — the cookies turn out best with a good chill.

Preheat the oven to 375°F. Sprinkle a little flaky sea salt or kosher salt over the top of each cookie.

Bake and check at 10 minutes. The recipe range is 12 to 14 minutes, but 10 gives a soft center with just-browned edges. Bake to your preference.

Let the cookies cool on the pan for a few minutes before moving them to a wire rack.