Step 1Heat the oven to 425 degrees. Line a baking sheet with parchment paper.
Step 2Rinse the fish thoroughly under running water; pat dry with paper towels. Place the fish on the baking sheet.
Step 3Combine the sea salt, flour and egg whites in a large bowl. In another bowl, toss together the thyme, tarragon, parsley, rosemary and dill. Set aside 1/2 teaspoon of the herbs for the vinaigrette, then stir the remaining herbs into the salt mixture. Cover the entire fish with the mixture, patting it firmly onto the top and sides of the fish.
Step 4Bake until the fish tests done, about 20 to 25 minutes. To check if it's done, use the tip of a small knife to break through the salt crust along the backbone of the fish at the thickest point. The fish should look opaque and easily pull away from the bone.
Step 5Remove the fish from the oven and let stand about 10 minutes. When the salt crust is cool enough to handle, gently crack it with the end of a knife, small hammer or mallet and remove. Peel the skin from the top of the fish. Lift the top half of the fish off the bone in large sections to a platter, then remove the center bone from the fish. Cut the meat from the bottom half into pieces and place on the platter.
Step 6Combine the lemon juice, olive oil, reserved 1/2 teaspoon herbs and salt to taste. Serve the vinaigrette with the fish.