1. Brown the butter by cooking it over medium heat in a medium saucepan until it’s amber to brown in color, about 5 minutes depending on pan size. Swirl the pan in the last minute or so to see the color changes. Butter will go through stages of hissing, sputtering, and making noise until the water cooks off, and the browning occurs. It should smell nutty and aromatic.
2. Pour the browned butter into a large mixing bowl, scraping the bottom of the saucepan with a spatula to transfer any browned bits. Let it cool a moment before adding the egg, so you don’t scramble it.
3. Add the egg, brown sugar, granulated sugar, and vanilla, and whisk to combine.
4. Add flour, cornstarch, baking soda, and kosher salt, and stir to combine. The dough may seem crumbly yet oily; this is okay.
5. Stir in the chocolate chips and pecans (lightly toast them if desired in a dry skillet until aromatic; however, un-toasted works fine too), and stir to combine.
6. Using a 2-tablespoon cookie scoop, or your hands, form about 16 equal-sized mounds of dough, roll into balls, and flatten about halfway. Tip: Put some chocolate chips and pecans on top for a visual pop.
7. Place mounds on a large plate or tray, cover with plastic wrap, and refrigerate for at least 4 hours, up to 5 days. Don’t bake with unchilled dough as cookies will bake thinner, flatter, and be prone to spreading.
8. Preheat oven to 350F, line a baking sheet with a Silpat or spray with cooking spray. Place dough mounds on the baking sheet, spaced at least 2 inches apart, and evenly sprinkle each with a generous pinch of sea salt, or to taste.
9. Bake for about 10 to 11.5 minutes (if your cookies are smaller than mine, reduce baking time) or until the edges have set, and the tops are just set, even if slightly undercooked, pale, and glossy in the center; don’t overbake. Cookies firm up as they cool.
10. Allow cookies to cool on the baking sheet for about 10 minutes before serving. It’s best to cool them on the baking sheet rather than using a rack.