Melt the butter and cream it with the brown and white sugar in a large bowl. Use a hand mixer or stand mixer.
Add both eggs and the vanilla extract and mix until just combined.
Sift together the flour, cocoa powder, salt, and baking powder. Or you can use a whisk. Add about half of it in with the other ingredients. Continue mixing with your electric mixer. Then add the rest of the dry ingredients in and switch to a wooden spoon. This ensures you don't overmix the cookie dough.
Cover the dough and allow it to chill for 3 to 4 hours or overnight. The chilling process helps to form the cracks on the cookies.
Scoop out the dough with a tablespoon or mini ice cream scoop or cookie scoop. Using clean hands roll the dough into a ball and then roll it in a small bowl of powdered sugar.
Place the cookie balls onto a baking sheet lined with parchment paper or a silicone mat and bake in a preheated oven at 350 F (176) for 10 to 12 minutes.
When they are done they should have nice cracks on top and will be a little soft. They will harden up while they cool down. But should not get too hard. Let them cool on the baking sheet for a few minutes then transfer to a wire rack to cool completely. Try and refrain from eating the whole batch, or don't. Enjoy!