In a large mixing bowl, cream the butter and sugars with an electric mixer on medium speed until light and fluffy.

Add the eggs one at a time, then pour in the vanilla extract. Scrape the bottom and sides of the bowl, and blend again until well mixed.

In another bowl, whisk together the flour, cocoa powder, baking soda, salt, and optional espresso powder.

Gradually mix the dry ingredients into the wet ingredients until just combined.

Stir in 2 tablespoons of milk and 1 1/2 cups of chocolate chips. If the dough is too thick, add more milk as needed to make it scoopable.

Cover the dough and chill it in the refrigerator for at least 3 hours, or overnight for the best flavor.

When ready to bake, let the dough sit at room temperature for 10-20 minutes.

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

Scoop the dough into balls about 2-3 tablespoons each and place them on the baking sheets, leaving about 3 inches of space between each cookie.

Press the remaining chocolate chips on top and sprinkle with sea salt, if desired.

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

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