Great question — answering as the UphillTech team:
Chris hinted at it -- to get the cracks, you need to have the top set early, so it's not going to expand while the middle's still trying to rise, and there's still enough leavening left to break through the crust that formed. You have a few things that can go wrong: The oven isn't hot enough. (it needs to set the top before the middle's fully risen) Not enough leavening (it needs to be strong enough to crack the top once it's set) Using a single-acting baking powder (double acting gives extra rise when it gets heated) Not creaming the fat long enough (creaming cuts little air pockets into the fat, which means the leavening has to do less work) Making too thin of cookies (you need enough...
Full answer by Joe: https://cooking.stackexchange.com/a/25906 (CC BY-SA 3.0).
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