I recently made some bar cookies and let them cool in their pan. They ended up on the dry side. Is there a time limit you suggest for allowing bar cookies to remain in the pan they were baked in?
I usually let bar cookies cool for about 10 minutes in the pan before transferring to a cooling rack. They're easier to remove from the pan while still warm, but boiling hot (ie. right out of the oven).
That's an interesting result. As HalfPint notes, a little cooling and then remove from pan is typically easier to remove than waiting until they are fully cold (although, I've learned to put parchment paper underneath, and then there are no removal issues, whether fully cool or otherwise). I'm puzzled, however, at a link between length of cooling and "dryness", and would think to look first at the recipe, not the cooling, for how dry the result was (unless the cookie was overcooked? Again, even in that case, the in-pan/out-of-pan cooling wouldn't change the texture...).
I will make a "basket" so that I can remove the bar cookies in case they need to be removed so they don't over cook. Lay one strip of aluminum foil across the pan leaving room to create flaps. Lay another strip the opposite way leaving flaps as well. Makes it way easier to get out if need be.
I use the "basket" technique for quick breads, too, and it works like a charm. I just use parchment, then trim it to just above the level of the pan so that it doesn't flop over and mar the surface of what I'm baking (learned that one the hard way). I agree with SeaJambon that they sound a bit overbaked. Bar cookies typically shouldn't be baked until solid (in other words, clean toothpick) in the center. If they are, the edges will likely overbaked. I use the tap test - tap with my fingertips in the center, and if it feels set but not solid, I take them out. You can always bake them longer, but it's difficult to unbake them.
Cook's Illustrated points out that leaving cakes and bar cookies in their pans too long can result in dryness, probably from overcooking from the hot sides of the pan. Cool them just long enough to stabilize the gluten-starch structure (10 minutes or so) then transfer to a rack to finish cooling.
Thank you all so much for your help!! I love this feature of Food 52. The thing is, I've made this bar cookie three times now - the first time they were stupendous. The second and third times too dry. I do think the only difference must be that I left them to cool longer the second and third times and that they were "baking" some more in the hot pan while they were cooling. I want to make half a batch next time just for experimental purposes, probably put in some parchment or foil to be able to lift them out after about 5 minutes. It's so disappointing to take all that time baking something to have it end up dry!!!
I usually leave the cookies until they are cool enough to be handled by hand, about 5 minutes.