I cook up some acorns every now and then when I find some big ones while hiking in the fall. Pick ones without worm holes (duh).

I cut them open with gardening shears and "grind" them in a blender to about the size of Grape Nuts cereal.
Mashing them in a rock hole is probably better to open up the
nut meat to rinse out the tannins easier.

Rinse with cold water a few times, then put 'em in a pot
with lots of water. Bring to a boil and let 'em sit for a few minutes, pour off as much water as you can. Repeat about 10-20
times until the water runs clear or until you can stand the
bitter taste. They're not bad! Kinda chewy, nutty tasting.
I put a heaping spoon of honey on them.

The water will stain a porcelain sink a nice brown, probably your teeth too! I use "Barkeeper's Friend" cleanser or "CLR" rust stain remover to clean the sink, works great. (I wouldn't use it on your teeth ;-)

Bye,
/////ANDRE