In a large bowl or stand mixer fitted with a paddle attachment, stir together the melted butter and coffee, let sit for a few minutes before adding the sugars and mixing together.
Add in the vanilla, egg, and egg yolk and beat until light and creamy, about 1 to 2 minutes on medium speed.
In a separate bowl, whisk together the flour, cocoa, baking soda, and salt. Add the dry ingredients to the wet ingredients in two separate additions, mixing between each one and scraping down the sides as needed.
Fold in the chocolate chips so they’re evenly distributed throughout the dough, then cover the dough in plastic wrap and chill in the fridge for 1 hour.
Preheat the oven to 325°F.
Measure the dough into ¼ cup-sized balls and rolls them between your palms before placing them on an ungreased cookie sheet, leaving at least 3 inches between each cookie.
Bake the cookies for 15 to 17 minutes, the centers will still look soft, this is normal since you will need to allow them to cool on the pan for 10 minutes after baking. Transfer to a cooling rack after 10 minutes to finish cooling or enjoy immediately.