Preheat oven to 375°F and line baking sheets with parchment paper.
In a large bowl, cream together butter and granulated sugar until fluffy using an electric mixer. Add the egg, brewed coffee, and vanilla extract to the butter mixture, beating at medium speed to combine.
With the mixer turned off, add all purpose flour, old fashioned oats, cocoa powder, baking soda and kosher salt.
Mix at low speed until mixture comes together, raise to medium speed, mixing until dough comes together. Mix in 1 cup of chocolate chips.
Use a medium cookie scoop to form evenly-sized dough balls. Place them about 2 inches apart on your prepared baking sheets.
Bake for 10-12 minutes or until edges are set but centers remain soft.
Lightly press additional chocolate chips into the warm cookies. Sprinkle lightly with flake salt if desired, to enhance the chocolate flavor.
Allow cookies to cool slightly on the baking sheet, then transfer to a wire rack.