1. Combine the kosher salt, coriander and fennel in a bowl.  Zest the lemon with a microplane and add it to the salt. Toss well to combine. Cut the zested lemon into thin slices
2. Season the inside of the fish with the spiced salt and some freshly ground white pepper
3. Put the lemon slices, with the thyme sprigs into the cavity of the fish
4. Whip the egg whites in a large bowl until foamy. Stir in the salt
5. Preheat oven to 400º
6. Lay a cup of salt on a baking pan, about ¼" thick. Lay the fish on top. Adjust the position of the salt and add more if necessary to ensure the fish sits completely on the salt. Cover with the remaining salt. Pat the salt to form a smooth sealed casing
7. Bake 30-40 minutes. Check the temperature of the fish. It should read 120º
8. Remove from the oven and let sit 5 minutes. Crack open the salt shell carefully by tapping with the back of a spoon.  Remove the top layer of salt
9. Working carefully, remove the fillets from the salt crust. First remove the skin and then the top fillet and put on a plate
10. Pick up the bone and discard
11. Carefully run a spatula between the bottom fillet and the skin and lift the fillet onto the plate. Remove any remaining bones
12. Serve with celery salsa verde

Celery Salsa Verde

1. Combine the parsley, celery leaves, tarragon, capers, anchovies and lemon zest in a food processor with ½ cup olive oil. Pulse to a coarse paste. It should not be a smooth puree.  Transfer to a bowl
2. Add the celery, garlic and lemon juice.  Season with salt pepper and mix until well combined
3. Mix in the remaining ¼ cup of oil if necessary.  Taste and adjust seasonings