If your chocolate brownie cookies didn't crack on top there could be a couple of reasons why. First, make sure the oven is heated to the correct temperature. Second, check that you measured your baking powder correctly or that it's not expired. Brownie cookies crack because the inside of the cookie puffs up when it bakes and breaks through the top. If the oven isn't hot enough, this won't happen. Or, if you don't add enough baking powder (or it's expired) the cookie dough won't puff up enough.