Make sure not to overbake these fudgy chocolate cookies with cocoa powder! Since they are made with a dark dough, you won't be able to use color cues to tell when they are done. They should look much less oily and shiny and have an almost matte finish. They will become more dense as they set, so don't move them from the cookie sheet until they are cooler. Also, don't try to make these cookies smaller than the recommended size! (Approximately 2½ Tablespoons - 48 grams.) I tested the recipe with both 1½ Tablespoon and 2½ Tablespoon cookie dough balls, and the larger size is what helps create the soft, fudgy center. I recommend baking a mini batch of 2 cookies on the first baking sheet so that you can confirm if the baking time works for your taste (and oven.)