This "book" is especially notable because it is illustrated by Edward Gorey (1925-2000), a writer and artist who was known for a distinct style that could perhaps be termed Victorian Gothic. (He categorized himself as "literary nonsense.") Gorey published more than 100 of his own books and is well known for his cover art and illustrations for a wide range of material, include the works of John Bellairs.1 He also provided the illustrations for the animated opening credits of PBS's Mystery! anthology.
Jack the Giant-Killer features 12 Gorey illustrations in its 10 fold-out pages. The folk tale, which first appeared in print in the early 1700s, is told economically, in just a few hundred words. (If you're interested in a longer version of the story, one author you could turn to is Ruth Manning-Sanders, who includes a version of the tale in A Book of Giants.)
If you're scoring at home, here's an updated ranking of the smallest books featured on Papergreat.
1. Warren's Pocket History of Winchester (2 inches wide)
2. Jack the Giant-Killer (2½ inches wide by 3½ inches tall)
3. Book of Brief Narratives (2⅞ inches wide)
1. For an example of Gorey's cover artwork, check out the 2015 post "Edward Gorey's fabulous cover art for The Wanderer."