1-In a large mixing bowl, cream the: 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, followed by the vanilla extract. Scrape the bottom and sides of the bowl, then blend again until combined.
2-In a separate bowl, whisk the flour,: In a separate bowl, whisk the flour, cocoa powder, baking soda, salt, and espresso powder, if using.
3-Gradually add the dry ingredients to the: Gradually add the dry ingredients to the wet ingredients and mix until almost combined. Stir in 2 tablespoons of milk and 1 1/2 cups of chocolate chips. If the dough is very thick, add more milk, as needed. It should be thick but scoopable.
4-Cover and chill the dough for at: Cover and chill the dough for at least 3 hours (or overnight) to allow the flavors to meld.
5-Let the dough soften at room temperature: Let the dough soften at room temperature for 10-20 minutes, then preheat the oven to 350°F. Line two baking sheets with parchment paper.
6-Scoop the dough into 2-3 tablespoon-sized balls: Scoop the dough into 2-3 tablespoon-sized balls and place on the prepared baking sheet, leaving about 3 inches of space between each cookie. Press the remaining chocolate chips onto the tops and sprinkle with sea salt, if using.
7-Bake for 12-15 minutes or until the: Bake for 12-15 minutes or until the edges are set and the centers are slightly soft.
8-Remove from the oven and let cool: Remove from the oven and let cool on the baking sheet for 5 minutes before transferring to a wire rack to cool completely. Serve and enjoy!