Everyone always thinks of mustard fish when Bengal comes to mind. Of course, Bengal has many kinds of fish and many uses for mustard oil (it controls dandruff too, did you know) but somehow the two are forever united in everyone's mind. When my friend landed up yesterday, that was on his mind too, so I complied.
New York doesn't really have great mustard fish. Most restaurants dont want to risk the distinctive taste of the real thing, so they offer a lowest-common-denominator watered-down version; the generic fish curry with a token mustard seed floating on top. Madhur Jaffrey's Dawat in New York claims it among its signature dishes but dont tell that to a Bengali.
Most other Indian restaurants are too busy cooking tikka masala to try anything different. The tragedy is, many are owned or run by Bangladeshis who really can make the real thing. The problem; mustard fish at it's best is threateningly mustardy (some should steam through your sinuses like accidentally eaten wasabi) and not for anyone who does not claim Bengali genes. On top of that, the gravy has to be greenchilly hot. How this mixture manages not to overpower the delicate smell of fish is one of the mysteries of wonderful food but, when done well, it's one of those things to die for. The fish melts in your mouth, the chillies dance on your tongue and the mustard steams up your nose - trust me, it's one of the better ways to heaven.
You would expect a region that cooks eveyrthing with mustard and eats fish by the zillion to have found more than one way to combine the two, and you wont be wrong. I was, however, not going to make a zillion kinds, so I shopped for some salmon and decided on one kind - "shorshe bata mach" (fish in mustard paste). Of course, temptation overtook me at the Grand Central market and I ended up with some sea bass as well, so I decided on two kinds of SBM (thats "shorshe bata mach" again) - seabass with nigella seeds (kalonji) and salmon with coconut milk. And, of course, small green Indian chillies (Habaneros won't work) and mustard paste. You can use other kinds of fish, but salmon works the best along with sea-bass and cod. The taste somehow fits the mustard.
The crucial part, of course, is the mustard paste. It's got to be strong, flavorful, and still look good. Modern technology comes to my aid here; ignoring the disapproval of my grandmother's ghost I head for Coleman's English Mustard which is the best - a good, strong, unadulterated mustard powder (most American brands have additives so watch out). Mix it with ice water, make it into a thin paste and let it soak for 10 min with some slit green chillies to give it a kick. This produces very nice mustard paste but one that's a uniform, boring yellow. What really livens things up is adding some freshground black mustard seeds - these have black skins that give it the flecked look of real Indian mustard paste. At this stage even my grandmother can't make the difference out.
Here's the rule; you cant cook mustard paste for more than a minute or so on boil because it starts to turn bitter after that. So you fry or pan-fry the fish (cut into medium cubes) till it's nearly done, and just boil it for sixty anytime seconds in the mustard paste. For the seabass, its nigella seeds in hot oil till they crackle, a small amount of poppyseed paste as thickener, the mustard paste and the fish, boiled for a minute before it's ready to serve. For the salmon, its coconut milk and mustard paste and fish all put into a pan and brought to boil for a minute - till the coconut milk just starts to thicken. Both versions can be prettied up with a touch of cilantro and served on white rice. A sprinkle of raw mustard oil on top is a good touch, and there you have it - SBM Coco and SBM Nigella.
Yes, really, thats it. If you've fried the fish to right done-ness, you now have melt-in-the mouth mustard fish in two varieties, ready to be hailed as that great Bengali chef you nearly are. Of course, you forgot the salt but that's another matter.