Brown the Butter and Toast Pecans: Melt the 2 sticks of butter in a light-colored stainless steel saucepan over medium heat. Swirl occasionally as it melts, foams, and crackles. After 5-6 minutes, foam subsides and golden-brown nutty specks form at the bottom with a toffee aroma. Immediately pour the browned butter and all browned specks into a heatproof bowl and let cool for 20 minutes to room temperature. Meanwhile, toast chopped pecans in a dry skillet over medium heat for 3-4 minutes until fragrant; set aside.

Whisk Brown Butter and Sugars: In a large mixing bowl, combine cooled browned butter, dark brown sugar, and granulated sugar. Whisk vigorously for 2 full minutes until the mixture looks glossy and emulsified. Whisk in the eggs, extra egg yolk, and vanilla extract until pale, smooth, and ribbons form when lifted.

Incorporate Dry Ingredients: Sift in the all-purpose flour, baking soda, cornstarch, and fine sea salt. Use a silicone spatula to gently fold just until a few streaks of flour remain (do not overmix, which would develop gluten and make the cookies tough).

Fold in Chocolate and Pecans: Add the chopped bittersweet chocolate chunks and toasted chopped pecans (reserving 2 tablespoons of each for topping the dough balls). Fold gently until evenly distributed throughout the thick, fragrant dough.

Chill the Dough: Cover the bowl with plastic wrap and chill in the refrigerator for at least 30 minutes (or up to 48 hours for even deeper toffee notes). Chilling solidifies the butterfat, preventing excessive spreading and ensuring sky-high bakery thickness.

Scoop, Bake, and Pan-Bang: Preheat oven to 350°F (175°C) and line two large baking sheets with parchment paper. Using a large 3-tablespoon (#20) cookie scoop, portion giant dough balls onto sheets 3 inches apart. Press reserved chocolate shards and pecan pieces onto tops. Bake for 10 to 12 minutes until edges are golden and set, while the centers look slightly soft and puffed. Immediately out of the oven, gently tap the baking sheet firmly on the counter twice to create crinkled ripples, then shower tops generously with flaky Maldon sea salt. Cool on the pan for 10 minutes before transferring to a wire rack!