Er, haha... actually it seems to have come out last year. The publisher is the usual Flying Eye Books, basé à Londres. What specifically excites me about this one is that it's evidently the first full Hilda GN to come out in five years! (I take it that author Luke Pearson spent most of that intermediate time working on the Netflix show) Also of note is that the story seems to be a prequel, which takes place before the first official story, i.e. 2010's "Hilda and the Troll".
Now, the "Hilda" books are nominally all-ages kids' fare, but to my mind, Pearson is incredibly clever about avoiding any of the typical, pandering traps that childrens' content-creators sometimes fall in to, not unlike say other kids'-lit geniuses such as Maurice Sendak and Dr. Seuss (well, more or less). My point is that as adults reading 'childrens books' like this, these are the kind of works that are deeply satisfying to read on many levels, and pull no punches in the scheme of things, so to speak.
Or something like that...
Here's an earlier sequence I shared a while back:
https://piefed.social/post/364368
I'd never heard of them, are they all self-contained or do you need to read them in order?
Hmm... I think they're mostly self-contained, implying that they can generally be read in any order. (except for the later 'stone troll' story, which is frankly kind of rough to read)
That said, I do think it makes the most sense to read them in order, provided you have opportunity.