The soupe au caillou? An old peasant recipe from Eastern France, especially Lorraine and Moselle. It’s a vegetables soup, with a "big stone" (caillou) inside. This stone, when vegetables are cooking, hits the bottom of the pot and crushes the vegetables little by little.
The legend says: one autumn evening, two monks stopped in a little village. They have eaten nothing since days! So they knocked at a house door, just in case.
Children opened the door, their parents were still working in fields. They said they had nothing for strangers, nothing to eat! Monks winced: those guys seemed a little stingy...
Kids finally welcomed them and lit a little fire. Oh, nice... but they wanted something to eat!! So, the two monks said they want to make a soup. "But there’s nothing to make it, hey", said kids. "Never mind", said one of the monks, "because it’s a stone soup I want to do. No need ingredients for that!" Kids were flabbergasted: stone?!
"Yes, of course, just give me water and a big washed stone and it will be fine..." Kids gave them. The pot started to boil, the stone inside. But this one wasn’t cooked! Monks blamed the water, because, usually, the recipe worked!
Oh, wait... we have to put salt... kids gave salt. Oh, we need a little slice of butter, too, and onions, cabbage, carrots... kids gave them all the ingredients, completely marvelled. "Aaah, now, you see, we’ve got our soup done!" said the monks.
And children brought them plates, bread, and our two wise guys could eat. They ate the soup, OK, but didn’t eat the stone!