Preheat the oven to 180°C (350°F). Line your baking sheet pans with aluminum foil, dull side facing up.
In a small bowl, sieve together flour, cocoa powder, baking soda and salt. Put aside.
Cream the butter in the bowl of your mixer on medium speed for about 2 minutes.
Add both types of sugar, granulated and soft brown sugar to the mixing bowl and mix for around 3 minutes on medium-highspeed until lighter in color and fluffy in texture.
Add an egg, vanilla extract, and coffee. Mix on low speed until combined.
Start adding the flour, cocoa powder, baking soda, and salt to the mixing bowl. While mixing on low speed, add two tablespoons of flour at a time, wait until it's incorporated into the batter, then add again. Scrape the sides of your mixing bowl with a spatula and give it a final mix.
Add the chocolate and mix on low speed until the chocolate chips are evenly spread in the batter.
Place the batter in the fridge for 10-15 minutes to chill the dough. It will make it much easier to form the dough into the balls.
Scoop out some of the batter using an ice cream scoop, and form it into balls with your hands. Each ball should be roughly 50-60g. This should give you between 12 and 14 cookies.
Place the cookie balls on the sheet pans, leaving some space in between the cookies, they will spread quite a lot during baking.
Bake until the cookie balls have spread flat on the sheet pan, but they are still slightly puffed in the center, around 7 minutes. Then take the sheet pan out of the oven, lift one side of it (not more than 10 cm, otherwise the cookies will slide down), and drop it down on the kitchen counter, repeat with the other side of the baking pan. Return it to the oven and bake for another 2 minutes, until the cookies puff up again. Repeat the whole process several times, bake for 12-14 minutes total.
Let the cookies rest on the sheet pan for 10 min and then transfer to a wire rack to finish cooling.
