In a medium-sized saucepan, melt the butter over medium heat until it turns a rich golden brown and gives off a nutty aroma, about 5-7 minutes. Remove from heat and let cool for 10 minutes.

While the butter cools, whisk together flour, baking soda, salt, espresso powder, and Vietnamese cinnamon in a large bowl.

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

Gently fold the dry ingredient mixture into the wet ingredients, stopping as soon as there are no visible flour streaks.

Fold in the dark chocolate chips evenly throughout the dough.

Cover the bowl with plastic wrap and chill the dough in the refrigerator for 45 minutes.

Preheat your oven to 350°F (177°C) and line baking sheets with parchment paper. Scoop the chilled dough onto prepared sheets and bake for 14-16 minutes.

After baking, let the cookies rest on the baking sheet for about 10 minutes, then transfer to a cooling rack for another 10 minutes.