Our allotment last year got slightly overrun with Fat Hen so before we dug it all out we decided to try our hands at collecting the seeds to make flour. Needless to say, this is hard work and not always worth the effort; nonetheless, they are an abundant seed available for a good portion of the year, and it was great getting to grips with the whole process of seed collection and processing. We waited for the fat hen to start turning a little yellow and collected the seed pods in bulk. It was then a laborious task to scrape all the seeds out and try to remove them from the plant husks. We tried various winnowing methods with limited success, but eventually as the husks dried, we found that firm rubbing on a wooden block followed by a gentle blow will do a pretty good job.
We added the ground fat hen seeds to bannock to test it out and it did very well. It might not be worth the bother of gathering it except in a crisis, but it was a very enjoyable and enlightening experience.