From the "Mission Poachable" episode of Alton Brown's "Good Eats" show on the Food Network.
The worst meal I ever had was a poached halibut, cooked by my grandmother for Sunday dinner. Grandma was a fine cook, and kept us all fed on a tight budget, but she was "shanty" Irish and had no feel for seafood or for poaching. It was such a disaster that I avoided poached ANYTHING for the next 40 years. Sorry, Grandma. But I was so impressed by this that I had to share it. (If it was anyone other than Alton Brown, I would never have tried it in the first place.)
You see, the problem with poaching fish is twofold: 1)there is a very narrow window of time and temperature for success with "conventional" poaching, (internal temperature should be about 140 F) and if you miss it, the results can be lamentable. Either the fish is undercooked (see above) or its completely dried out. Yes, moist heat can dry out fish faster than an oven broiler. And there is no easy way to judge where that window is, except with a instant read or digital probe thermometer, which most of us don't have.
2) Food safety issues demand that the poaching liquid must be at a boil for at least a moment or two to kill any lingering bacteria in the fish. But 212 is way too hot for decent poached fish. And when you back off the heat on an oven burner, how far down are you supposed to go? "Overshoot" or "undershoot" are impossible for a novice to judge and time, ESPECIALLY using an electric range.
Brown's solution: Use an electric skillet to bring the poaching liquid to a boil, put the fish in it for 30 seconds or so, and then bring the temperature setting of the skillet down to 140-145 F. After 7-9 minutes, the fish will be safe, perfectly done and it will stay that way for 20-30 minutes - without drying out. Voila, the 'window' is now wide open and the size of a 45 lb Clubbell®!
Pour one can evaporated milk in an electric skillet. Add 2 TB "Old Bay" seasoning (or some other "crab boil" mix), 1/2 of an onion (thinly sliced), several grinds of fresh black pepper from your grinder, and a bit of kosher salt.
Bring the poaching liquid to a boil. When it is bubbling gently, add the fillets (anywhere from 1-5 depending on your appetite) to the liquid. If there is not enough to cover, that's OK, just spoon some milk over the fillets. After 30-40 seconds, back the setting of your skillet down to 140-150, cover the skillet and simmer for 7-9 minutes (a little more time for more fish, a little less if you are only doing one or two). Remove and plate, spooning a little of the sauce over the fillet. Serve with rice, a salad, etc.
I've tried this with halibut, catfish, sea bass, and tilapia, and it seems to work great for any delicate white fish fillet. The (slightly sweet) evaporated milk seems to blend nicely with the oils in the meat, and (like most properly poached dishes), can be served cold in a buffet, etc. Coconut milk might work even better, but I haven't tried it yet.
I'm dead certain that you could also poach salmon and other oilier fish with this method, but perhaps not with this particular liquid. Every poached salmon recipe I've seen recommends a dill based sauce, which I haven't gotten to yet.Maybe court-bouillion would also work (see below).
If you are a little more ambitious (and I was, I used it on sea bass), you can also make "court-bouillion" as a poaching liquid. This is a French concoction of onions, carrots, celery, white wine, etc. It's well worth the effort, but court-bouillion isn't a 15 minute project (although it can be reused, unlike the evaporated milk ), so I won't go into it here.
Hope this helps those of you trying to add sea food into your diet, but are sick of canned tuna and can't afford lobster.