To cure the salmon (1 side):
Mix the sea salt and citrus zest thoroughly in a bowl. Spread a wide sheet of cling film out, place half the salt mixture on it then lay the salmon on it. Cover with the rest of the salt mix, wrap tightly in the cling film and chill for 12 hours, flipping it over half way through. 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, 1 side will provide about 12 portions.
For the potato:
Slice the potato on a Japanese mandolin 1.5mm thick. Lay four slices on top of each other at a time then punch out coins with a pastry cutter, 3cm wide. Cover a microwave proof plate in cling film. Starting on one side of the plate, place onecoin of potato, then take one coin at a time, dip 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 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 greasproof paper, sprayed with spray-wax. Cover with another piece of parchment and cling film, store in the fridge for 1 day.
Garnish:
place the smoked asparagus trim in a medium sized pan and add the cream, pepper lemon, bring to the boil then remove from the heat, infuse for 30 minutes. Pass though a fine chinois and press the cream through thoroughly into a measuring jug. Heat the cream and dissolve one leaf of softened gelatine per 150ml of cream. Transfer to piping bags to cool. Tie off the end then refrigerate until needed, remove form the fridge about 20 minutes before using to soften slightly.
To Serve:
Brush the salmon portion with egg white, lay a portion of potato over this and press down.
Heat a non stick fish pan, add a small amount of olive oil. Place the fish in to the pan, potato side down. Pan fry for 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 180c for 1 minute.
Lay a spear of asparagus (or baby leek) across the top and bottom of each plate (brushing them first with olive oil to shine them) then pipe three small points of the halibut cream onto each. Dress each point with a pearl of keta and sprig of dill. Place the salmon on the plate between the two then serve at once.