Note, that unlike what was said in the Manga, boiling potatoes does not remove the solanine nor chaconine. The compounds concentrate in the skin, so peeling the potatoes is sufficient to get rid of most of the compound and the resulting tuber is very edible raw.
Make sure to discard the tubers that are green under the skin.
This would be correct if he referred to the standard potato from the Solanaceae family. However, he did not; he clearly stated that they are "konnyaku potatoes", which is another name for the Elephant Yam, otherwise known as Konjac, which produces the corm that is processed into the gel of the same name. One of the primary issues with the Konjac corm is that it contains calcium oxalate, which is, in fact, a toxic substance that is broken down when cooked.
That aside, I'm surprised no one in the comments was enthusing over the puffed-up brat cheeks of the elf, lol.