Brown the Butter: In a light-colored saucepan over medium heat, melt unsalted butter. Swirl frequently as it foams and crackles. After 5 to 7 minutes, tiny amber milk solids will form at the bottom with a fragrant toasted aroma. Pour immediately into a mixing bowl and let cool for 15 to 20 minutes.

Toast Pecans & Whisk Dry Ingredients: Preheat oven to 350°F (175°C) and line two large baking sheets with parchment paper. Toast chopped pecans in a dry skillet over medium heat for 3 minutes until aromatic. In a separate bowl, whisk together flour, baking soda, and fine sea salt.

Beat Sugars & Eggs: Add dark brown sugar and granulated sugar to cooled browned butter. Beat with a whisk or electric hand mixer for 2 minutes until glossy. Whisk in whole egg, egg yolk, and vanilla extract until the mixture turns pale, silky, and thick.

Fold Dough & Bake: Stir in dry ingredients just until combined. Fold in dark chocolate chips and toasted pecans. Scoop 2-tablespoon dough balls onto baking sheets 2.5 inches apart. Bake at 350°F (175°C) for 10 to 12 minutes until edges are golden and set, and centers remain soft. Immediately sprinkle with flaky sea salt while hot. Let rest 5 minutes, then cool on a wire rack!