"Between the ribs." Entrecôte steak. A lean, tender steak cut from the thin end of boned sirloin. It is a thick, juicy, well-marbled steak and is excellent for grilling and is a classic French steak.
I was told this was butterfish, but the very dense (yes, buttery) compressed white flesh had the appearance of hake or swordfish or similar. It was certainly from a much larger, meatier fish than a butterfish. Escolà is the Catalan for ling. Does this help?