How to toughen cookies I have a problem with my cookies becoming crumbly as they hang-out in room/warm afternoon temperatures.

I bake cookies -- a lot for fundraisers. Normally these cookies are stored in display cases within main halls and sold by students. What happens whenever I test them in the middle of the day, is that they've lost their tender toughness, which is more akin to a freshly baked batch or one from the refrigerator.

Since the cookies won't be sold through a refrigerated display-case for the foreseeable future, I wonder what's a good ingredient to make the cookies tougher within warm ambient temperatures? I suppose grocery-store cookies have this certain ingredient to a higher extent.

Thanks for your help!

The recipe is as follows

(Makes 120-130 cookies)

Wet:


1 lb butter (2x 220g), caramelized/browned to 300 F -- cooled
10 oz granulated sugar + 4 eggs + 4 tsp vanilla extract
10 oz brown sugar


Dry:


20 oz APF
6g baking soda, 8g iodized salt
2 tbsp corn starch
16 oz dark chocolate chips*


*I should disclose this. I use couverture chocolate chips so they're slightly melty, but also because they're cheaper than bakeproof ones.
I'd imagine these are being stored in a simple glass / plastic display similar to what you'd see at a sari-sari store. 

Shalryn's suggestion is good, but it compromises the quality of the cookie a bit. I'd look at using some sort of desiccant first, and a simple electric fan behind the display to move the air around in order to take advantage of it. Humidity and lack of air movement is definitely a big problem here, and if you can find a way to control that, you might not have to alter the recipe (which sounds positively delicious and I'm going to try it).

Some rice flour in a small shallow tin might just be enough to do it. You'd have to experiment a bit, and ultimately you might have to alter your recipe, but those cookies are surely a hit and I'd hate to see you have to make them harder for logistic's sake :)  

If they're being sold in boxes, just add a silica gel pack and let folks know that they can't hit direct sunlight for too long. They are incredibly cheap (they run around 1.25 pesos from anywhere between 2-3 gram packets).