Hoffmann's next story collection was his longest and possibly my favorite: The Serapion Brethren, published in four volumes from 1819 to 1821. It had a strange, lovely format. In it, Hoffmann collected his recent, unpublished stories and novellas, together with (I think, though I'm not 100% up on the publication history of each of his short stories) some unpublished ones, but gave them quite an extensive narrative framework: it concerns a group of four friends (and later five, as they vote to add one more to their group) who get together regularly to read to each other their writings, then to discuss them, reflect on them, and so on. So Hoffmann distributed his stories among these several fictional personas, and also got them to discuss his own literary productions. Actually, these dialogues in the framing narrative (including further tales the friends tell each other) are some of the best parts of the book. The most famous story in this collection is, by far, "The Nutcracker" (and, if you were puzzled by the story of the ballet, if you read Hoffmann's original telling you'll realize that's only half the story, and the backstory provided makes everything much clearer), but it also includes such well-known pieces as "Madame de Scuderi," "Signor Formica," 'The King's Betrothed," "The Mines of Falun." "Doge and Dogaressa," and "Councillor Krespel," a.k.a. "The Cremona Violin," one of the sources for Offenbach's great opera, The Tales of Hoffmann.
There is one full (and quite good) translation of the entire book, by Major Alex. Ewing, in two volumes, London: George Bell and Sons, 1886, 1892. The bad news is copies of it are extremely rare. (But I managed to snag a set, finally!) The good news is it's available for free on Kindle, with relatively few typos. I should add that, in translation, between the two volumes, it's almost 1100 pages. Most of the stories I mentioned above can be found in other more recent collections in translation, but for a number of the tales this is the only translation; also, this is the only translation of the framing narrative, which really brings the stories together into a unified work.