It's autumn, and that means that it is time to start gathering acorns to make acorn flower. Hank Shaw has a great guide to making acorn flower over on his site, honest-food.net:
Every year I learn more about working with acorns, but each year I come to more and more conclusions. The latest is that there is really only one good way to make quality acorn flour: Cold leaching.
Wha? Leaching, as is pulling something out. In this case, that something is tannin, which in almost all acorns is there in spades. Different acorns have different levels of tannins, but in general oaks of the red oak family have more, the white oak family less. One, the Emory oak of the Sonoran Desert, has almost none at all.
Before I go much further, let me answer the question in many of your minds: Why the hell would I bother making flour from acorns? First, flavor. It’s a lot like chestnut flour: Nutty, a little sweet and just generally interesting. Second, nutrition. Acorns vary in nutrition. Some are very starchy, some oily, a few high in protein. Third, it’s just kinda fun to make something useful and tasty out of something many of us mistakenly believe is poisonous.
For my two cents, I'll suggest using Quercus macrocarpa (bur oak) acorns. They are large and in the white oak sect, so they have fewer tannins. Once you have your flower all ground and dried, why not try making some Acorn Maple Shortbread Cookies?