It's a 2016 comics adaptation by Colleen Doran of a 1993 short story by Neil Gaiman. The original was first published in Snow White, Blood Red, an anthology of re-imagined fairy tales, then got reprinted in a 1998 Gaiman collection, Smoke and Mirrors.
I haven't read the original, but this adaptation's quite good. I liked it.
It starts out so personal that it feels autobiographical. The protagonist (called Jack, as is right and proper for a fairy tale) talks about the closure of railway stations in the early 1960s, which is true and happened due to the Beeching reports. The dates line up with Gaiman's real childhood, incidentally. It looks as if both he and Jack were born in 1960 and would have similar memories. All this establishes a real-world context that's utterly convincing, especially when Jack goes wandering in the countryside.
I grew up in a place like that. It's true. This isn't even fiction, let alone fantasy. I could show you abandoned railway lines and bridges just like the ones Jack remembers here. Also, Colleen Doran's art is so true to what's in my head that I was surprised to learn that she's American.
Despite the book's title and a look at the troll on p1, I was surprised when Jack met a troll under a bridge.
I won't spoil the rest of the story. It's conversational, easy to read and narrated in the first person past tense. It shows us different ages in Jack's life. It shows us darkness. (The relatability of that first pseudo-autobiographical phase of the story makes that more affecting than it would have been otherwise.) It shows us an oddly trusting troll. It has a memorable ending.
This book must have been successful, because in 2019 Colleen adapted another Gaiman story from Smoke and Mirrors. That one's called Snow, Glass, Apples and it won awards. I've bought a copy. I'll report back.