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 to see the color changes. The butter will smell nutty and aromatic.
2. Pour butter into a large mixing bowl, making sure to scrape the bottom to transfer any browned bits from the bottom into the bowl. Wait a moment before adding the egg.
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, which is okay.
5. Add the chocolate chips and pecans, and stir to combine.
6. Using a cookie scoop or your hands, form about 16 equal-sized mounds of dough, roll into balls, and flatten halfway. Add a few 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.
8. Preheat oven to 350°F, line a baking sheet with a Silpat or spray with cooking spray, and place dough mounds on it, spaced at least 2 inches apart. Sprinkle each with a generous pinch of sea salt.
9. Bake for about 10 to 11.5 minutes, until edges have set and tops are just set. Don’t overbake.
10. Allow cookies to cool on the baking sheet for about 10 minutes before serving.
