Melt unsalted butter in a medium saucepan over medium heat, stirring frequently until golden brown and nutty, about 5-7 minutes. Remove from heat and cool slightly.

In a mixing bowl, whisk together the all-purpose flour, baking soda, salt, espresso powder, and Vietnamese cinnamon. Set aside.

In the bowl with cooled brown butter, blend in granulated sugar, dark brown sugar, and light brown sugar until smooth.

Add the egg and vanilla extract to the sugar mixture, stirring vigorously until smooth.

Fold the dry mixture into the wet ingredients until just combined, then add the dark chocolate chips.

Cover the cookie dough with plastic wrap and refrigerate for 45 minutes.

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

Scoop mounds of dough onto prepared baking sheets, spacing them 2 inches apart. Bake for 14-16 minutes until edges are lightly browned.

Allow cookies to rest on the baking sheet for 10 minutes before transferring to a wire rack to cool for another 10 minutes.