This is really easy. It takes a bit, but it's really easy. I don't have a grain grinder or nut grinder, so I have to use my blender. I'm sure it's even easier with a grinder!
Making Chickpea (garbanzo bean) flour:
1. Get some dried chickpeas. Wash them and then spread them out to dry again.
2. Put a couple medium sized handfuls in a blender.
3. Turn the blender to the setting for grinding up really hard foods, like the ice crusher setting.
4. Blend for a few seconds, I usually do 10-20 seconds. When the flour starts getting fine, it can get stuck at the bottom of the blender, start to heat up, and affect your blender, so don't do it for too long.
5. Pour the ground up chickpeas through a mesh sieve and into a clean bowl. Shake the sieve a bit to sift out the finer pieces, and then pour the larger pieces (still in the sieve) back into the blender.
6. Add another small handful of dried chickpeas to the blender with the half-crushed chickpeas and blend.
7. Repeat steps 4 through 6 until all the chickpeas are blended up and sifted through the sieve. I usually end up with a little at the end that can't get any finer. These, I put in a mortar and pestle and finish off, or add them to something else to cook with.
This flour is coarser than garbanzo bean flour you can buy at the store, so it won't always work for all recipes that call for chickpea flour. However, it works quite nicely for the flatbread Socca. This bread is from France, and from what I read, it is usually made with a coarser chickpea flour than you find in the USA, anyway. :-)