Preheat oven to 375°F. Line baking sheets with parchment paper.
Bring a small pot of water to a boil. Place the bittersweet or unsweetened chocolate in a heat proof bowl. When the water comes to a boil, remove it from the heat. Place the bowl of chocolate over the hot water. (The water should not touch the bowl.) Allow to sit for 3-5 minutes, then stir until the chocolate is fully melted. Remove the bowl from over the pot, wipe the bottom of the bowl dry, and set aside.
In a small bowl, whisk together the flours, cocoa, salt, baking powder, baking soda and espresso powder (if using). Set aside.
In the bowl of an electric mixer, cream together the butter and sugars. Beat for a minute or two until the mixture is light and fluffy. Mix in egg and vanilla until fully combined.
Add the melted chocolate to the butter/sugar/egg mixture and beat until fully combined.
Mix in dry ingredients just until fully combined. Stir in chocolate chips.
Portion and mound the cookies into 30 gram balls, flattening each slightly. Place on prepared baking sheets, about 2-inches apart. Top each cookie with additional milk chocolate chips. Bake for 8-10 minutes. Cool for a few minutes, then remove the cookies to a wire rack to cool completely.