How to Make It
Preheat oven to 400º. Whisk the egg whites until peaks form. Fold in the salt, rosemary and thyme and set aside.
Spread the lemon slices and fennel out on a baking sheet. Place the fish over the lemon and fennel, skin side up. Pour the egg white mixture over the fish and spread to cover completely.
Bake until a knife goes into the fish easily and it is cooked through, 20-25 minutes. Remove from the oven. Crack the salt crust and peel away in large pieces. Separate the meat from its skin and transfer to serving plates. Top with a drizzle of olive oil.