Run your fingers from head to tail to locate the fish’s fine pin bones and
remove using needle-nosed pliers or tweezers. Stir together the salt and sugar. Lightly crush the coriander and fennel seeds together in a mortar. Add to the salt-sugar mixture with the lemon zest. Stir to evenly distribute.
Line a tray with plastic wrap. Sprinkle the tray with ½ cup of the curing
mixture, making a bed with even thickness as large as the filets would be if placed side by side. Arrange the fillets on the bed of seasoning, skin side down. Sprinkle each fillet with ½ cup of the curing mixture. Sandwich the fillets, flesh sides together, then wrap tightly in plastic wrap. Put a tray on top and a 5-pound weight on the tray. Refrigerate for 3 days, turning the package over each day.
Unwrap the fish and inspect the flesh. It should feel firm but not leathery. If it still feels flaccid, rewrap, replace the weight, and marinate another day longer.
To serve, unwrap the fish and scrape off the spices. Rinse the flesh briefly in cold water, then pat it dry. Using a thin-bladed knife, carve the fish as thinly as possible on a strong bias to make wide slices. Serve with garden carrot pancakes and crème fraiche pickled mustard seed.
Enjoy with a glass of Cakebread Cellars Cuttings Wharf Chardonnay