I live in Thailand in which potatoes in retail supermarkets can be a bit expensive because of a bit low demand due to low traditional usage in local cuisine. In my opinion in Thai bazaars the price is likely to be a bit lower though. Although, it would be hard for me to make these in my apartment as I don't have much tools in quite small kitchen, in which I have an electric stove with small pot and common sized pan.  I desire to make a vegan instant potato puree like course. In Thailand, as in the rest of the world, instant Potato puree like courses are commonly sold ready to eat by "add hot water and heat" method in "convenience stores" and I consider to prepare something similar with potato starch by my own because I find these instant courses unhealthy (filled with synthetic materials with doubtful effects on human health and also expensive).  Using potato starch might be good for me because people use it to make non traditional cakes in this country and it is likely to be sold online in large quantities for small businesses (although I am a single buyer) and could be mixed with ingredients and cooked fast.  To clarify problem I'm trying to solve is making a vegan potato based or primarily potato based Potato puree; desirably without using whole potatoes (or with using a small amount).  Notes   I never found dried potato flakes in local stores in my area but online shopping might be a good alternative Any other staple food (rice/corn/semolina, etc) doesn't necessarily do with the problem I am trying to solve   My question  I assume potato starch (which is of course just the starch and not the whole potato) would be a basic ingredient of a potato puree like course and if so, what else do I need besides potato starch, for making a vegan potato-puree like course without whole potatoes? 
This seems like a bit of a catch-22.   If you bake the assembled gingerbread house for an extra 90 minutes at 90°C, the gingerbread cookies will possibly/likely become dried out, hard, and inedible.   Candies and decoration may become similarly dried out and inedible. Some chocolate or gummy candies may melt, even at the relatively low oven temperature.   I wouldn't consider baking the completed gingerbread house as a means to make it edible. I think it would have quite the opposite effect (though, I've never done it).  I think the real question is whether the raw egg whites used are safe to consume as is. As mentioned in one of the comments, this can vary depending on where/how the eggs are sourced and what country's regulations you're listening to. Here in the US, the FDA warns against eating raw eggs, but US eggs are quite different than European eggs due to the differences in cleaning/processing eggs between the farm and table.  