Adjust racks to center and lower-third position and preheat oven
to 350°. Line 2 large baking sheets with parchment. In a small
bowl, combine espresso powder and milk and stir until dissolved.
In a large bowl, whisk together flour, cocoa powder, baking soda,
and salt.
In another large bowl, whisk together butter and sugar. Add eggs
and whisk until lightened in color, about 2 minutes. Add espresso
mixture and vanilla and whisk until combined. Add dry ingredients
and stir until just a few dry streaks remain. Add chocolate chips
and stir until just combined. Using a medium cookie scoop (about 3
tablespoons), scoop dough onto baking sheets about 2” apart. Top
with flaky sea salt.
Bake until edges are just set, 10 minutes. Let cool on baking
sheets for 10 minutes, then transfer to a cooling rack to let cool
completely.
