Cooking fish inside a salt crust is very traditional. The salt insulates the fish from the extremes of heat, ensuring it cooks evenly and seals in all the flavours and juices. It also makes for a dramatic centrepiece if you crack it open at the table. And no, the fish won’t taste salty – the scales protect the flesh so it remains sweet and succulent. You can use this type of cooking for most types of fish, though it’s not ideal for oily varieties such as salmon and mackerel.
Season the stomach cavity of each fish, then sprinkle in the fennel seeds and arrange the lemon slices inside.
Mix the salt with about 100ml water until it starts to resemble wet snow. Place a 2cm layer of the salt mixture in a roasting tin and sit the fish on it top to tail. Cover them with the remaining salt, patting it down to make sure there are no gaps.
Place in the oven for 25 minutes, or until the fish are just cooked through and smell aromatic, and the salt has formed a hard crust.
Crack open the salt crust by hitting it with the back of a spoon, then carefully lift it off. Peel off any skin remaining on the fish. Using the edge of a spoon, run it down the middle of the flesh and gently push each fillet away from the bones: they should come away easily.