Black cod at Rasika. Miso black cod at Nobu. Both amazingly buttery and the highlight of the meal. Where can I find this fish for purchase in the DC area? That is, where can I buy it raw and cook it myself?
Look for sable or sablefish. Not sure that black cod is actually codfish.
Another name is butterfish but there's an East Coast fish that goes by that name so that might get you off track. Local butterfish is terrific but usually small, looks like a tiny pompano or John Dory. Same shape as a flounder but it swims upright.
Call Black Salt on MacArthur Blvd., Southern MD Seafood at Eastern Market on Capitol Hill, or Slavins in Alexandria.