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 and sugar until light and fluffy.
Add the egg and vanilla, mixing until combined.
Gradually add the dry ingredients, alternating with milk, until a soft dough forms.
Fold in the hazelnuts and chocolate chips.
Scoop tablespoon-sized portions and roll into balls.
Place cookies 2 inches apart on the baking sheet.
Slightly flatten each ball with your fingers.
Bake for 10-12 minutes, until edges are firm but centers are soft.
Let cool for 5 minutes, then move to a rack (or straight to your mouth).