If you were looking for the oddest dish being served in an American restaurant right now, you should probably start with the fish course at Jordan Kahn's new Vespertine, a dish that nudges the idea of culinary abstraction dangerously close to the singularity. It doesn't look like fish, for one thing -- it looks rather like an empty bowl, coarse and pebbly inside and out, of a blackness deep enough to suck up all light, your dreams and your soul. If this were Coi or Alinea, to name two modernist temples, your server would instruct you on how to eat the dish, or at least on where you might direct your spoon. At Vespertine, the server, wearing a severe frock like something out of "The Handmaid's Tale," does not. If you prompt her, she may whisper the word hirame, which in a sushi bar can mean either flounder or halibut.