Bengali cuisine from eastern India and Bangladesh is the great fish cuisine of the subcontinent — built on freshwater fish from the Ganges delta, mustard in all its forms (oil, seeds, paste), and a unique five-spice blend called panch phoron. The relationship between Bengalis and their fish is as culturally significant as the French relationship with wine or the Japanese with rice. Shorshe (mustard) preparations are the pinnacle: fish steamed or simmered in a paste of freshly ground black and yellow mustard seeds, green chillies, and mustard oil. The combination produces a sharp, pungent, nasal heat that's unlike any other cuisine's spice profile.
Panch phoron (five-spice): equal parts fenugreek, nigella, cumin, black mustard, and fennel seeds — used whole, tempered in mustard oil as the first step of most Bengali dishes. The five seeds are never ground. Mustard paste: soak yellow and black mustard seeds in water for 30 minutes, then grind to a smooth, pungent paste. The paste is raw and aggressive — cooking it mellows the harshness but should retain some bite. Mustard oil: heated to smoking point (to dissipate the harsh raw compounds), then cooled slightly before use. This 'smoking' of mustard oil is essential — unsmoked mustard oil tastes acrid. Fish is typically cut into steaks (not fillets) because bone-in pieces hold together during cooking and add flavour.
Shorshe ilish (hilsa fish in mustard) is the crown jewel of Bengali cuisine — hilsa (a bony, oily river fish) steamed in banana leaf with mustard paste, green chillies, mustard oil, and turmeric. The oily fish stands up to the aggressive mustard. If hilsa is unavailable, mackerel or salmon work as substitutes because of their fat content. For beginners: start with shorshe maach using any firm white fish — the mustard paste technique translates to any protein. The Bengali approach to vegetables is equally sophisticated — potatoes fried with panch phoron and turmeric (aloo bhaja) is a daily staple and deceptively simple.
Using Western prepared mustard instead of grinding seeds — completely different product. Not smoking the mustard oil — raw mustard oil tastes harsh and unpleasant. Using fillet instead of bone-in steaks — the bones are integral to the dish. Cooking the mustard paste too long — it should retain some sharpness. Using dried mustard powder — fresh ground paste has volatile compounds that powder lacks.