While yes it is possible for such a soup that appears such a way to contain Potatoes let me show you why in fact it is impossible for Emilia to have obtained Potatoes in order to even make the soup. (A THREAD) https://twitter.com/ReadTsukihime/status/1280919533570711552

First of all, as shown in this image Emilia lives in a forest, and as Puck says the Forest is always either Cloudy or Sunny. According to https://www.thespruce.com/growing-potatoes-in-the-home-garden-1403476#:~:text=To%20keep%20the%20top%20growth,or%20they%20will%20turn%20green Potatoes IDEALLY require full sunlight to grow, while they can handle partial shade it is unlikely anyone would...

grow potatoes in such an environment since it also as Puck says constantly snowing. According to https://www.hunker.com/13428241/how-to-plant-potatoes-in-florida severe cold can inflict serious damage to potatoes, and while yes snowfall can occur at 32 degrees Fahrenheit, such constant snowfall and a cold climate...

likely sustain temperatures far below 32 degree damaging Potatoes. So it's clear no one, nevertheless Emilia will be farming Potatoes, and that's already debunked by Puck who states that her food is generally secured by the village. So I know it was already clear that Emilia...

or the village wasn't growing Potatoes but I wanted to debunk that before I moved on. So in order to craft a Potato soup Emilia must trade with the merchant who likely receives his wares from outside the village. Though shown in these two shots Emilia largely buys what...

looks like an assortment of nuts (the crescent shaped nut clearly being a cashew) and we never are shown that she is trading for potatoes. In this shot as well we see the wares of the store and absolutely no indication of any kind of Potato. So in conclusion in order to make...

such a soup Emilia must've used rocks she found in the forest (I posit that they must be sedimentary rocks formed by glacial drift, a glacier that very much may exist a cold climate such as Emilia's forest). It's likely that she grew sick of constantly eating nuts and made...

some Rock Soup to change up her diet and introduce some much needed minerals.