In a small saucepan over medium heat, melt and swirl the butter until golden‑amber and fragrant. Remove from heat immediately and stir in the espresso powder. Let cool slightly then strain through a fine‑mesh sieve into a mixing bowl (“browned butter method”)

Add brown sugar and granulated sugar to the warm butter mixture. Stir until combined, then whisk in the egg, yolk, and vanilla extract until smooth

In a separate bowl whisk together flour, baking powder, baking soda, and salt. Gradually stir into the butter mixture just until no streaks remain. Fold in chocolate chips or chunks

Chill dough 15–30 minutes if desired (for thicker cookies), though not required

Preheat oven to 350 °F (175 °C). Line baking sheets with parchment paper. Scoop dough into 2–3 Tbsp balls spaced ~2″ apart.

Bake 10–14 minutes until edges are golden but centers still look soft. Remove from oven, let cool on sheet 2 minutes, then transfer to rack to cool completely