If you have any doubt on the freshness/quality of your salmon, freeze it first then defrost it before making the gravlax to get rid of any bacteria. If it has been previously frozen or is sushi grade, no need to do this.

Trim any thin pieces from your salmon. They will likely over-cure and are best used in some other way fresh. Carefully check to see if there are any bones and remove. Cut the salmon in two equal-sized pieces. This can be down the central spine if a wide fillet so you have in effect two squares.

Mix together the cure of salt, sugar, pepper, dill and lemon zest in a small bowl.

Place one of the pieces of salmon, skin side down, in a dish just larger than the piece of salmon, and tip the cure over the top. Spread evenly.

Place the other piece of salmon on top, skin side up. It should be the opposite way round from the bottom piece if possible (ie if bottom piece is thick on the left, have the other piece thick side to the left. Rub any cure that's escapes out the sides on the side and over the top of the salmon.

Cover the fish with plastic wrap/cling film and place in the fridge. Put another dish or plate on top weighed down with something heavy (I used a few beer cans!). Leave it to cure, turning every 12-24 hours for 2-3 days until the salmon goes firm and slightly opaque.

Rub off any excess cure (some stray dill is fine) and pat the fish dry. Slice the salmon thinly across the grain, removing any skin, and serve.