To cure the salmon (1 side):
Mix the sea salt and citrus zest thoroughly in a bowl. Place half the salt mixture on a wide sheet of cling film and lay the salmon on it. Cover with the rest of the salt mix, wrap tightly in the cling film and chill for 12 hours, turning it over half way through. After 12 hours, wash off the salt. Remove the skin carefully ensuring the blood line comes away as well. Trim off the excess from the belly (keep this for tartare for canapés, etc.). The width of the salmon loin should be around 9cm across, or as desired. Cut 3cm wide portions. Chill until needed. One side will provide about 12 portions.
For the potato (about 5 portions, 2 pieces per portion):
Slice the potato on a Japanese mandolin 1.5mm thick. Lay four slices on top of each other at a time and punch out coins with a pastry cutter, 3cm wide. Cover a microwave proof plate in cling film. Place one coin of potato on one side of the plate then, one at a time, take each coin dipping a quarter of it on the potato starch then lay this on the potato coin already on the plate. Continue, to give a line of potatoes containing 8 overlapping and connected pieces. Start the next line of potatoes, continue until you have covered the plate. Cover with cling film, taking care not to disturb the lay out. Pierce all over with the tip of a small knife. Microwave for 1.5 to 2 minutes or until the potatoes are just soft and steamed. With a small palette knife, lift the potatoes portions, one at a time, onto a tray lined with greaseproof paper, sprayed with spray-wax. Cover with another piece of parchment and cling film and store in the fridge for one day.
Oyster sauce:
Sweat the shallot and tarragon stalks in butter, adding a little salt at the outset. Heat gently until soft, add the vermouth and reduce by half. Add oysters and their juice and poach for one minute. Add the milk and cream, heat quickly and remove from the heat, add a small amount of lemon juice. Blitz in a thermomix until you get a smooth consistency. Taste and adjust as required then set aside.
Charred cucumber:
Combine the water, star anise, vinegar and sugar and heat to dissolve the sugar, this will make more than is needed for one recipe but can be stored in the fridge. Heat a small amount of the pickling liquor then keep warm to pickle the cucumber. Char the cucumber in a very hot pan on one face until very dark then keep warm in the pickling liquor.
To Serve:
Brush two pieces of salmon per portion with egg white, lay a portion of potato on each salmon and gently press down to aid adhesion.
Heat a non stick fish pan, add a small amount of olive oil. Place the fish into the pan, potato side down. Pan fry for 1 - 2 minutes or until the potato is golden. Carefully turn over with a fish slice then remove at once. Place onto a tray and transfer to the oven and cook at 180°c for 1 minute.
Arrange two pieces of salmon in the middle of the plate. Place the cucumber around the outside. Finish with sea herbs and some caviar, if desired. Heat the oyster sauce, add finely chopped chives and transfer to small sauce jug to be poured at the tableside.