Preheat oven to 350°F (175°C). Line a baking sheet with parchment paper.
In a bowl, whisk together flour, cocoa powder, baking soda, salt, and espresso powder.
In another bowl, beat butter, brown sugar, and granulated sugar until fluffy.
Add egg and vanilla to the butter mixture, mixing until smooth.
Gradually mix in dry ingredients until combined.
Fold in pecans and chocolate chips.
Scoop dough onto the baking sheet, spacing cookies 2 inches apart.
Bake for 12 minutes, or until edges are firm but centers remain soft.
Let cookies cool on the sheet for 5 minutes, then transfer to a rack.
Enjoy immediately or store in an airtight container.