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 mass in the middle so it finishes cooking after the top's set).
- Mixing the dough too much (you don't want to develop gluten; it needs to be tender enough to crack easily)
As Jennifer mentioned -- old baking soda can be a problem. I'd also consider investing in an oven thermometer to make sure that it's really providing the temperature the dial claims, as those are the two things that are going to be the most difficult to judge if they're a problem or not.
You'll also want to make sure the oven is properly pre-heated (so it doesn't loose all its heat when you open the door to put the cookies in), and avoid opening the door again 'til it's time to pull them. If you have to rotate them (as the oven cooks unevenly), do it as quickly as possible so the oven's not open for very long.
The original author is in error adding baking soda (bicarbonate), and indicating it will help rise. For leavening, you require acid for the sodium bicarbonate to react with. The original base recipe has no significant acid ingredients; even the modified version you used has only a trivial amount of acid from the molasses in the brown sugar.
Therefore, the only effect of the baking soda is to increase the pH of the dough, which will encourage browning. However, as the cookies are full of sugar, encouraging browning is not generally a problem.
The creaming method creates bubbles in the solid phase butter, and encourages rising and a more cake-like result, especially when paired with an effective leavening agent.
Resting the dough also hydrates the flour, and allows the butter to re-solidify, both of which inhibit spread and contribute to a higher cookie.
For a chewier result, do not use the creaming method. Melt the butter instead, and then combine your ingredients.
You may also choose to reduce the baking soda to reduce the metallic taste it brings without anything to react with.
If the cookies are now too dense, you might try adding (starting with smaller amounts) 1/2 tsp to 1 tsp or so of baking powder which has its own acid to react with, to help leaven the cookies.
See also:
Best Answer
In general, to create crispier cookies:
baking soda (if you use this to replace the baking powder, keep in mind it's thought to be 3x as strong, so reduce accordingly. The decrease in acid leads to a longer set temp, which will help your cookie bake to be crispier. If you'd like to even out the decrease in acid, you can always use a little bit of each, or even add in a little lemon juice)
replace the egg (with whole milk to encourage spreading)
make sure the butter you're creaming is at the right temperature (read this post for more info: http://blog.kingarthurflour.com/2015/04/27/creaming-butter-sugar/)
bake it for longer at a lower temp with smaller flatter cookies
All of these tips are meant to increase the surface area of the cookie exposed to the heat, in order to dry it out/crisp it up. However, your cookie recipe also has the addition of all the water and stickiness of the fruits, so it is unlikely that you can get it to be completely dry and crispy, like a sugar cookie, for instance.
Tips gathered from many sources and experience, but the best one for cookies found was this one: http://blog.kingarthurflour.com/2015/04/27/creaming-butter-sugar/
Good luck on our quest for crispier fig cookies!