Don't know about edibility. But if you want to save the seeds, let the heads mature on the plant, remover the whole head and leave it to dry in a dry place - I've use the greenhouse before now. The seeds should start to loosen in their holders and after a while turn the head over alarge piece of paper and shake the seeds out. Winnow then to remove detritus & then store in sealed packets if you want to use for growing. I ave also stored them as bird food.
You shouldn't need to cook them to eat. If you do want to, I would dry roast them.. You could also press them for the oil - I would imagine you need a lot to get a decent amount of oil.
"For to be free is not merely to cast off one's chains, but to live in a way that respects and enhances the freedom of others." - Nelson Mandela