So I was buying Vitelottes.
Then I put them in a bucket with potting soil. Except for an infection with plant lice and watering them from time to time, I mainly had to wait. Then a few days ago, I dug them out. I found some nice things, like this huge maggot:
It might become a chafer - I am not sure about its species, if somebody knows, feel free to send me an e-mail. I just covered it with soil again, after digging out the potatoes. Speaking of which:
Sorry for the bad quality of the photos.
I would call that a success.