Oliver Jeffers still keeps a workspace in Brooklyn, where he lived for 17 years before returning to his native Belfast to be closer to family during the pandemic. When I meet the author and artist in his studio on a drizzly afternoon—a few hours before he’ll recite an original poem at a gala for the UN General Assembly—it’s awash in paint-splattered amusements. In one corner sits a ghost, a sheet with eyeholes that Jeffers proudly says glows in the dark and “really freaks people out.” On a ceiling-high chalkboard, written in his signature scrawl—a cross between a child’s handwriting and a ransom note—his list of tasks begins: “Glue moon.”