Preheat the oven to 220°C.
Cut the fennel into 4 pieces, remove the core and cut thinly slice. Roughly chop the green sprigs from the fennel bulbs. Peel the spring onions and cut into fine diagonal slices. Finely chop the spring onion stalk.
In a large saucepan or pot, sweat the onions with a drizzle of olive oil and a pinch of salt. Add the fennel then pour in water to half the height of the vegetables. Cover and cook for 5 minutes. Add the chopped spring onion and the 5 spices then check the seasoning.
Mix the salt with the egg whites to make a paste. Spread the salt paste on to a baking tray, lay the sea bass on top and cover with more of the salt. Transfer to the oven and cook for 18 minutes. Remove from the oven, break the salt crust and remove the sea bass. Take out the fillets and season with piment d'Espelette.
Serve the sea bass on a bed of braised fennel. Garnish with the chopped fennel sprigs and serve immediately.
«Avoid using salt that has been overly idiosed as this will prevent the salt from forming a paste.»