Begin by gathering all your ingredients, ensuring that the unsalted butter and large eggs are at room temperature. Preheat your oven to 350°F (175°C) and line two baking sheets with parchment paper.

In a large mixing bowl, beat the room-temperature butter with granulated and brown sugars using an electric mixer on medium speed for about 2 to 3 minutes until creamy and light in color.

Add the large eggs one at a time into the creamed mixture, mixing well after each addition. Stir in the vanilla extract.

In a separate bowl, whisk together the all-purpose flour, cocoa powder, baking soda, and salt. Include espresso powder if using.

Gradually add the dry mixture to the wet ingredients, mixing on low speed until just combined. Stir in milk if the dough is dry or crumbly.

Cover the cookie dough with plastic wrap and refrigerate it for at least 2 hours, or ideally overnight.

Preheat your oven to 350°F (175°C) if you haven’t already. Prepare your baking sheets lined with parchment paper.

Using a cookie scoop or spoon, portion out the chilled dough and roll into balls about 1.5 inches in diameter. Place them on the baking sheets, spacing them apart.

Bake for 10 to 12 minutes until edges are set and centers look slightly underbaked.

Allow the cookies to cool on the baking sheets for 5 to 10 minutes before transferring to a wire rack to cool completely.