Start by melting the unsalted butter over medium heat in a light-colored saucepan, allowing you to monitor its color. Once melted, reduce the heat to medium-low and continue cooking until the butter turns a golden brown, releasing a nutty aroma—this should take about 5-8 minutes. Remove from heat and let it cool for 10 minutes.

In a medium bowl, whisk together the all-purpose flour, baking soda, salt, espresso powder, and Vietnamese cinnamon. Set aside the dry mixture while you focus on the wet ingredients.

In a large mixing bowl, add the cooled brown butter, granulated sugar, dark brown sugar, and light brown sugar. Whisk them until smooth and creamy, then add in the room-temperature egg and vanilla extract, mixing until fully incorporated.

Gently fold the dry mixture into the wet ingredients using a spatula. Once no streaks of flour remain, add the dark chocolate chips, folding them in until evenly distributed.

Cover your mixing bowl with plastic wrap and refrigerate the cookie dough for at least 45 minutes.

While the dough chills, preheat your oven to 350°F (177°C) and line two baking sheets with parchment paper.

Once the dough has chilled, use a 2-tablespoon scoop to portion out the dough, shaping each scoop into a ball. Place the cookie dough balls on the prepared baking sheets, spacing them about 2 inches apart.

Bake the cookies in the preheated oven for 14-16 minutes, until the edges turn light brown while the centers still appear slightly soft. Remove the trays from the oven and cool on the baking sheet for 10 minutes before transferring them to a wire rack.