In a medium saucepan over medium heat, melt the unsalted butter, stirring continuously. Reduce heat to medium-low and cook for an additional 5-7 minutes until golden brown. Remove from heat and cool to room temperature.

In a large mixing bowl, whisk together the all-purpose flour, baking soda, salt, espresso powder, and Vietnamese cinnamon until no lumps remain. Set aside.

In the bowl with cooled brown butter, add the granulated sugar, dark brown sugar, light brown sugar, egg, and vanilla extract. Mix until smooth and creamy.

Gradually add the dry ingredient mixture to the wet ingredients, folding gently with a spatula until just combined.

Fold in the dark chocolate chips evenly into the cookie dough.

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

Preheat your oven to 350°F (177°C) and line two baking sheets with parchment paper.

Using a cookie scoop, drop mounds of dough onto the prepared baking sheets, spacing them 2 inches apart. Bake for 14-16 minutes until edges are golden brown.

Allow cookies to cool on sheets for about 10 minutes before transferring to a cooling rack to cool completely.