Get the fish gutted and cleaned from the flakes when you buy it, if possible. Otherwise make an incision in the belly, remove all the inners and scrape away all flakes from the skin with a knife. Wash your fish well. Stuff the belly of your fish with any herb you like or which is available. I personally prefer fresh thyme, but this is difficult to find. Dried oregano or rosemary is also good. Take whatever you fancy.
Tear a sheet of aluminum foil from the roll which is big enough to wrap around your fish and the salt. Place the aluminum foil on a cookie sheet and spread half of the salt over the bottom. Place your fish on the salt and cover it with the remaining salt. Your fish should be covered an all sides by sea salt. If the fish is really big, you might need more than 2 kilograms of salt. Now close the aluminum foil around your fish and bake it in the oven for 45 minutes at medium heat. If your fish is very big, you need to increase the cooking time for 10 to 15 minutes. When the fish is done, put it with the aluminum foil on a big platter and bring it to the table. Dissect the fish directly at the table and serve it. The skin of the fish will stick to the salt which makes cleaning the fish easy.