I've seen this method of cooking fish twice in the last month. Firstly, by Daniel Humm of Eleven Madison Park in New York; secondly, by Adam Byatt on Saturday Kitchen. Daniel applies it to Black Bass and Adam to Sea Bass, but the method could be used for any similar, firm, meaty fish. I'm guessing flatfish wouldn't be that suitable and, for me, salmon and trout are better confited. Many vegetables, such as potatoes, beetroot, and celeriac are salt-baked, with equally delicious results.
The sea bass in this recipe is coated in a mixture of egg whites and salt to protect it from the heat, making it less easy to overcook the flesh. Daniel wraps the fish in crepes before applying the egg/salt mix so that the salt does not fall onto the fish when cutting off the crust. In my experience this isn't essential, since the skin, which is removed after cooking, will catch any falling salt.
So, to start, mix roughly 500g of salt (regular table variety) with enough egg white to give the consistency of wet sand (that is to say, make it spreadable but not runny). It might seem like a lot of salt, but it only costs 30p for a tub and, have no fear, the salt is not going to penetrate the fish.
Then, get your gutted, de-scaled an de-finned fish, and stuff the belly cavity with thyme, lemon, dill, or whatever you fancy. Spread a little of the mixture on a non-stick tray or silicone baking mat, sit the fish on top, then coat with the mixture using a spatula/palette knife (see below). You can make decorations in the salt crust a la Daniel Humm, but it's obviously extra work and not necessary.
Place the bass in an oven at 220 degrees Celsius for 15 minutes per kilogram. My fish weighed about 800g so that's 12 minutes. Remove from the oven and check the temperature. I use a digital thermometer to test doneness - for, me between 45 and 50 degrees Celsius is optimum. The more you go above 50 degrees the flakier and drier the fish will become.