Wash the cockles under cold, running water.
Preheat the oven to 60°C. Wash and zest the orange. Mix the orange zest with the fleur de sel and then spread this mixture on to a baking sheet. Transfer to the oven and cook for 20 minutes to dry out the mixture.
Peel and finely dice the onion. Sweat the onion in a saucepan then add the cockles and the white wine. Cover and cook until the cockle shells have opened - this will only take a few minutes; discard any cockles that have not opened. Remove the cockles from the pan and de-shell. Reduce the cooking liquid and then add the cream. Pass through a fine sieve and season to taste.
Wash the celeriac and the sweet potato then peel and cut into 1cm cubes. Place the vegetables in a wok and enough water to cover 3/4 of their height then add the butter. Add the seasoning, cover and cook over a high heat for a few minutes. Finish cooking without a lid, allowing all the liquid to evaporate.
Wash and pick the coriander.
Preheat the oven to 160°C.
Season the fillets of cod with freshly ground pepper and a little of the orange salt. Place on a baking sheet with a little olive oil then cook in the oven for 8 minutes.
Whilst the cod is cooking, place the coriander leaves and the cockles in a bowl and season with orange salt, olive oil and white balsamic vinegar.
Blitz the shellfish sauce with a hand blender to make it frothy.
Make a square or rectangle of vegetables and then place a fillet of cod on top (removing the skin before serving). Drizzle the shellfish sauce over the cod and finish with a few fresh coriander leaves.
«If you would like to serve this dish with a thicker shellfish mousse, add a pinch of soya lecithin to the sauce and serve using a syphon.»