In a large mixing bowl, beat the butter with both sugars until light and fluffy, about 2-3 minutes. Add eggs and vanilla, mixing until combined.

In a separate bowl, sift together flour, cocoa powder, baking soda, salt, and espresso powder. Whisk thoroughly.

Gradually stir the dry mixture into the wet mixture until just combined. If the dough feels dry, add a splash of milk.

Fold in chocolate chips until evenly distributed. You can add nuts or other mix-ins if desired.

Cover tightly and refrigerate the dough for at least 3 hours or overnight.

Preheat your oven to 350°F (175°C). Line two baking sheets with parchment paper.

Scoop the dough into balls and place them on the baking sheets about 2 inches apart. Press extra chocolate chips on top if desired.

Bake for 12-15 minutes or until edges are set and centers are soft.

Allow cooling on baking sheets for about 5 minutes before transferring to wire racks.