Properly prepared fried food is light and virtually greaseless. Fish should be fried in fat heated to 365°F. A deep-fat thermometer is essential for testing the temperature of the fat. If the cooking temperature is too low, the fish coating will absorb the fat and the fish will taste greasy. Conversely, if the temperature is too high, the coating will burn, and the fish may not cook through, depending on its density.
We recommend dipping all food to be fried in cold buttermilk and then in a fried fish coating. Of course, you could use milk, but buttermilk adds a richer flavor. Then shake off any excess mixture and deep-fry the fish in preheated oil until it's cooked through but not overdone. It's important to fry only a few pieces at a time so the pan does not get overcrowded. When it does, the oil temperature decreases and the food becomes oily, has trouble browning and cooking evenly, and will be limp, not crisp. It's best to butterfly any thick fillets.
You could also use wet batter, as the English do with their fish and chips. We've experimented with this technique but keep coming back to soaking the fish in buttermilk and then coating the pieces with a dry mixture. This method keeps the fish crisp yet juicy, because the fish steams in its own juices, which the batter seals in, and the flavor is retained.
No matter how you fry the fish, serve it immediately. Otherwise the fish will become soggy, as the steam released from the interior softens the coating.
From the "Legal Sea Foods Cookbook" by Roger Berkowitz and Jane Doerfer, illustrated by Edward Koren.