The dish gets its jet-black color from technique, not food coloring — beef shoulder is fried in mustard oil and a heavy spice blend for so long that the meat itself darkens almost to char.
Beef is browned in mustard oil with a long list of whole and ground spices, then fried down slowly until the gravy reduces to a thick, near-black coating clinging to the meat. It began as a Chattogram specialty and now shows up at weddings, Eid tables, and mezban feasts nationwide.