Preparation Steps

• Brown the butter: Add the butter to a light-colored saucepan and cook over medium heat, stirring, until the milk solids turn golden and it smells nutty, 3–5 minutes. Transfer to a large mixing bowl and let cool until warm, not hot, 5–7 minutes.
• Preheat the oven to 325°F (165°C). Line two baking sheets with parchment paper.
• Bloom the cocoa: Whisk the cocoa powder into the warm browned butter until smooth and glossy.
• Whisk in the sugars until combined. Beat vigorously for 30 seconds, rest 2 minutes, then whisk again for 30 seconds to help the sugars dissolve slightly for a shiny top.
• Whisk in the egg and vanilla until the mixture is thick and satiny.
• In a separate bowl, whisk together the flour, baking soda, cornstarch, espresso powder, and salt. Add this dry mixture to the cocoa mixture and stir with a spatula just until no dry spots remain. Let the dough rest 10 minutes to hydrate.
• Fold in the chocolate chips, reserving about 2 tablespoons of chips for topping the warm cookies later.
• Scoop 2-tablespoon portions (about 40g) and arrange 2 inches apart on the prepared sheets. Lightly flatten the tops with your fingers.
• Bake 12–14 minutes, rotating the pan at 8 minutes and rapping it once on the oven rack to encourage crackly tops. Cookies are done when the edges are set and centers look slightly soft.
• Immediately dot the hot cookies with the reserved chips. Cool on the sheet for 5 minutes, then move to a rack to finish cooling.