01 - Place butter in a saucepan over medium heat. Melt, then cook, swirling frequently, until butter foams, smells nutty, and brown bits form at the bottom (about 5–7 minutes). Remove from heat and let cool for 10 minutes.
02 - In a medium bowl, whisk together flour, baking soda, salt, and espresso powder until well combined.
03 - In a large bowl, combine cooled brown butter, brown sugar, and granulated sugar. Beat until smooth and glossy.
04 - Add eggs one at a time, mixing well after each addition. Stir in vanilla extract until fully incorporated.
05 - Gradually add dry ingredients to wet ingredients, mixing until just combined. Do not overmix.
06 - Fold in chocolate chips or chopped chocolate until evenly distributed throughout the dough.
07 - Cover dough and refrigerate for at least 1 hour, up to overnight, for optimal flavor and texture.
08 - Preheat oven to 350°F. Line two baking sheets with parchment paper.
09 - Scoop 2-tablespoon portions of dough (about golf ball size) onto prepared sheets, spacing 2 inches apart.
10 - Bake for 11–13 minutes, until edges are golden and centers are just set. Optionally sprinkle with flaky sea salt while warm.
11 - Let cookies cool on baking sheet for 5 minutes before transferring to a wire rack to cool completely.