Cut into two fillets that will sit on top of each other.
Rub salt in the skin of both fillets.
Lay one salmon fillet in a wide shallow dish that fits the salmon snugly, skin side down.
In a bowl mix together the salt, sugar, English mustard and vinegar to make a yellow slush.
Spread this mixture over both of the salmon's pink flesh, covering well.
Roughly chop the dill, and then pat the herb down onto the paste-covered salmon in the bowl.
Press well so that no pink from the salmon is visible.
Turn the other fillet over and press down on top of the first.
Cover the salmon with a piece of cling film, press it into the sides but leave the base clear for juices to escape.
Cover the dish with one layer of cling film and then do another layer of cling over that.
Place another dish over the salmon and weigh the it down with jars, tins or any other weights you can find.
Place in the fridge for 2-3 days.
Unwrap the dish and lift the salmon fillet out of the liquid it will now be lying in.
Rub off and discard the dill to expose the pink salmon, and lay on a carving board flesh side up.
Working from the right hand end of the fish (unless you're left-handing), carve very thin diagonal slithers with a long, sharp knife.
Don't worry about the uniformity of the slices; instead try to get them as thin as possible. The fish skin helps you to carve, as it will give you something to run your knife along as you go.
Remove the skin as you slice.
Re-wrap in cling film and keep the gravlax steeping in the fridge if it is not all sliced in one go.
