Shorshe Ilish

The flagship dish of Bengali cuisine on both sides of the border (West Bengal and Bangladesh), eaten especially during monsoon when Hilsa runs upriver to spawn (June–September). Recipe is documented in 19th-century Bengali cookbooks but is much older — Hilsa worship and ritual eating predate written records and are tied to Durga Puja and Bengali New Year.

Hilsa fish in mustard paste — the dish that Bengalis fight Bangladeshis over. Padma-river hilsa (Bangladesh) wins on fat content; the paste needs both yellow and black mustard or it goes one-note bitter.

Hilsa fish steaks plated in a thick mustard-yellow paste — coarse-ground brown and yellow mustard seeds, green chili, a slick of mustard oil, sometimes a drop of nigella. The fish is rich and oily (Hilsa is the fattiest river fish in South Asia); the mustard cuts straight through. Eat with a mound of plain rice; bones come out by hand on the plate.

Mustard paste must be ground with green chili and a pinch of salt — the salt is non-decorative; it deactivates the myrosinase enzyme that turns mustard bitter when ground alone. Skip the salt and the paste develops a back-of-throat acridity within minutes. Steaming or light simmering is the only correct heat: high heat or long cooking makes mustard taste burnt and the Hilsa fall apart. The whole dish cooks in under 15 minutes.