I'm referring to this recipe:
From the molly yeh gingerbread house article
this recipe here with the egg whites? https://food52.com/recipes...
I'm eager to learn the official answer to this too. The gingerbread recipe I'm working from (one that comes with those gingerbread house molds) has a similar icing recipe, and they say it can be stored at room temperature - for how long, they don't say.
I suspect it needs to be airtight. The Molly's recipe for the icing says the cling wrap needs to be touching the surface of the icing for storage.
So now we know how to store it, all we need to find out is how long we can store it.
You can make it the day before, but it only takes a few minutes to make, and for me making it fresh it would be worth it to avoid losing a portion of the icing to the plastic wrap you need to press down on the surface to keep the icing from drying out. When I was growing up we had two Christmas trees - one "regular" tree and a "cookie tree". The cookie tree was decorated with small ornaments, sugar cookies and gingerbread men wrapped in plastic. We decorated the cookies with total icing and always stored the leftover icing in the refrigerator with plastic directly on top of the icing. I've read that you can store it for up to a week, but I remember it getting pretty hard after a few days.
Royal icing, not total icing. Spell check strikes again!