I first got the idea from http://www.paul.fr/produits/us_ephemeres.htm
I ground roasted chestnuts (bought from a stall) and used it for the bread since chestnut flours are not available here.
About 25% ground chestnuts with 30% rye & washed with egg white.
The roasted chestnuts imparted a natural sweetness and actually tenderised the dough. So the crumb was soft without the addition of fats / sugar. Sure to try it again! :)
*PS: Pair with a dark full bodied honey... ;)