Preheat the oven to 350°F/175°C. Line two baking sheets with parchment paper.
Start by creaming the sugar, butter, eggs and vanilla extract in the bowl of your stand mixer or using your hand mixer and separate bowl, until light and creamy.
Combine the flour, cocoa, baking soda and salt in a separate bowl, and mix well.
Carefully stir the dry ingredients into the wet ingredients. You will want to do this carefully to prevent the dry part to blow out the bowl in large clouds.
Add the chocolate chips and stir until evenly distributed.
Baking
Pinch off dough and create a ball. The size is up to you: an inch of rounded dough will give nice small cookies, while about 2 inches worth will give the size you know from well-known sandwich shops.
Bake the cookies for about 12-15 minutes. Larger cookies will take closer to the 15 minute-mark. When done, they will still be soft. Allow them to cool on the baking sheet before moving them to a cooling rack to cool completely.
If you prefer to offset the cocoa taste with something sweet, mix 100 grams of icing or confectioner's sugar with a few drops of water and stir into a thick mixture. When the cookies are completely cool, transfer the icing into a disposable piping bag and cut off a small corner. Moving slowly across, create a line over the cookie. Repeat for all. Allow the icing to dry before stacking the cookies.