Preparation Steps

• Brown the butter: Melt the butter in a light-colored saucepan over medium heat. Cook, stirring often, until the milk solids turn deep golden and smell nutty, 4–6 minutes. Immediately scrape everything (including the browned bits) into a large mixing bowl to cool for 5 minutes.
• Whisk the dry ingredients while the butter cools: In a separate bowl, combine flour, cornstarch, baking soda, fine sea salt, and espresso powder.
• Blend sugars into the warm brown butter. Whisk in the brown sugar and granulated sugar until a glossy paste forms, about 1 minute. Let the mixture stand for 5 minutes, then whisk again briefly to help the sugars dissolve.
• Add egg and vanilla. Whisk until the mixture looks smooth, thick, and slightly lightened, 30–45 seconds.
• Fold in the dry ingredients with a spatula just until mostly combined; a few floury streaks are fine. Stir in 1 cup of the chocolate, reserving the rest for topping.
• Quick-chill the dough: Pat the dough into a 3/4-inch-thick slab on a piece of parchment, cover, and refrigerate until the edges feel firm and the center is scoopable, 20–30 minutes. If the dough still feels very soft, chill 10 minutes more.
• Preheat the oven to 360°F (182°C). Line two sheet pans with parchment paper.
• Portion: Scoop 1 1/2-tablespoon mounds (about 30 g each), roll into balls, and arrange 2 inches apart on the pans. Gently press a few of the reserved chocolate pieces on top of each ball.
• Bake 9–11 minutes, rotating the pan once, until the edges are set and lightly golden while centers look soft. For crinkly edges, bang the pan once on the rack at the 8-minute mark and finish baking.
• Cool the cookies on the pan for 5 minutes, then transfer to a rack to finish cooling. If you love a salty finish, sprinkle a tiny pinch of flaky sea salt on the hot cookies (optional).