The salt in this recipe forms a hard crust as it bakes, infusing the fish with moisture and flavor.
Heat oven to 450 degrees. Rinse fish thoroughly inside and out until no traces of blood remain. Pat fish dry with paper towels.
In a large bowl, stir together salt and egg whites until thoroughly combined. Place a 1/2-inch layer of salt mixture in the bottom of a 13-by-9-by-2-inch baking pan. Place lemon rounds, parsley, thyme, and bay leaves on top of salt, arranging ingredients so they form shape of fish and reserving some of each ingredient. Fill fish cavity with reserved lemons and herbs; place the fish on top of mixture.
Pour the remaining salt over fish, completely covering the body; the tail can stick out of the pan. Using your fingers, pat down salt, completely sealing the fish.
Place pan in center of oven. Cook fish until done, allowing 15 minutes per pound. (One way chefs check for doneness is to insert a carving fork or metal skewer through the salt crust and into the fish, then place it to the chin under lower lip for 15 seconds; if the metal feels very warm, the fish is done.) Remove pan from oven; let sit 5 minutes.
Gently break away crust. Transfer fish to a cutting board. Using a paring knife and your fingers, peel away skin. Separate, and serve.
You can use any small fish, such as sea bass.