There is no end to what you can shove between two slices of bread and call a sandwich, and that, of course, is the beauty of the thing. But is everything edible suitable sandwich material?

That was the point brought up for debate the other night at El Quinto Pino, the new taperia from the Tía Pol folks, where the UG tucked into a ficelle smeared with rich blobs of sea-urchin roe. Oddly, the sandwich in question was listed on the otherwise all-Spanish chalkboard menu as an “uni panini.” It came swaddled in a wax-paper jacket like a Danny Meyer Shackburger, still warm from a gentle turn in the sandwich press and smeared with butter flavored with a zingy Korean mustard oil. And although it was only about the size of a Tootsie Roll and the UG could have finished it off in a bite and a half, it was the kind of toothsome tidbit you want to savor slowly.