In a small bowl, combine the warm brewed espresso and stir in the espresso grounds. Set aside to cool.
1 tablespoon brewed espresso, 2 teaspoon espresso grounds
In a stand mixing bowl, cream together the butter and brown sugar on low until fluffy.
6 tablespoon unsalted butter, ⅔ cup light brown sugar
Add in the egg yolks and mix until well combined. Scrape down the bowl with a spatula.
2 large egg yolks
Add in the cooled espresso and grounds and vanilla and mix until combined.
1 teaspoon vanilla extract
Add in the flour, baking soda, salt, and chocolate chips and mix until just combined.
1 cup all-purpose flour, ½ teaspoon baking soda, ¼ teaspoon salt, ⅓ cup dark chocolate chips or chopped chocolate
Scoop the dough with a large (¼ cup) cookie scoop onto a parchment-lined baking tray spaced 2-3 inches apart. Top each ball with extra chocolate if desired. Freeze until solid, about 15-20 minutes while the oven preheats to 350 F/180C.
Bake the cookies for 12-13 minutes, or until the edges are just barely golden brown but the middle is still soft and gooey.
Let the tray cool on a wire rack completely before removing the cookies. Sprinkle with flaky sea salt if desired and enjoy!
flaky sea salt for topping