In a large mixing bowl, cream the softened butter, white sugar, and brown sugar using an electric mixer on medium speed until light and fluffy (about 2-3 minutes).

Add the eggs one at a time, followed by the vanilla extract. Scrape the bottom and sides of the bowl, then blend again until really combined.

In a separate bowl, whisk together the flour, cocoa powder, baking soda, salt, and espresso powder (if using).

Gradually add the dry ingredients to the wet mixture. Mix until almost combined. Add 2 tablespoons of milk and 1 1/2 cups of chocolate chips. If the dough feels too thick, add more milk to achieve a thick but scoopable consistency.

Cover the bowl with plastic wrap and chill the dough for at least 3 hours (or overnight for enhanced flavors).

After chilling, allow the dough to soften at room temperature for 10-20 minutes.

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

Using a cookie scoop, scoop the dough into 2-3 tablespoon-sized balls and place them on the prepared baking sheet, at least 3 inches apart.

Press the remaining 1/2 cup of chocolate chips onto the tops of each cookie and sprinkle sea salt, if desired.

Bake the cookies for 12-15 minutes, or until the edges are firm but the centers are soft. The cookies will continue cooking while they cool.

Remove the cookies from the oven and let them sit on the baking sheet for 5 minutes before transferring them to a wire rack to cool completely.