Preheat the oven to 400ºF (200ºC). Line two baking sheets with silpats or parchment paper and set aside.
In the bowl of a stand mixer with the paddle attachment affixed, add the chilled coffee-infused butter from recipe above, brown sugar and granulated sugar.
1 cup dark brown sugar , ½ cup granulated sugar
Beat on medium speed for 3-4 minutes until light and fluffy.
Stop the mixer and scrape down the sides and bottom of the bowl with a rubber spatula.
Add the egg and egg yolk and mix on medium speed for another minute until fully incorporated.
1 large egg, 1 large egg yolk
With the mixer off, scrape down the sides and bottom, then add the espresso powder, vanilla and brewed espresso.
1 teaspoon espresso powder, 1 teaspoon vanilla extract, 1 tablespoon freshly brewed espresso or strong coffee
Mix on medium until incorporated. With the mixer off, add in the flour, baking powder, baking soda, and salt.
2 ¼ cups all-purpose flour, 1 teaspoon baking powder, 1 teaspoon baking soda, 1 teaspoon salt
Stir on low speed just until incorporated, stopping to scrape down the sides of the bowl as needed.
Add in the chopped chocolate and stir just until incorporated.
2 cups dark chocolate
Using a ¼ cup (2 ounce) cookie scoop, scoop dough onto prepared baking sheets, about 6 per sheet, spacing dough about 2 inches apart.
Gently press chunks of dark chocolate into the tops of each cookie.
In a small bowl, mix together the espresso powder and flaky salt and sprinkle liberally on top of each cookie.
1 tablespoon espresso powder, 1 tablespoon flaky sea salt
Bake in a preheated oven for 5 minutes, rotate baking sheets and continue baking for 5 minutes more or until cookies are starting to turn golden brown at the edges and no longer look raw in the middle.
Remove from the oven and allow to cool for at least 10 minutes on the baking sheets. Optional: use a large round cookie cutter to circle around each cookie immediately after removing from the oven. This helps create perfectly round cookies.
Move cookies to a cooling rack and bake remaining cookies.