Prepare the cure: Add the salt, sugar, half of the dill, and the zest of 2 lemons to a food processor. Blend for about 1 minute until you have a bright green, slightly wet cure. Check the salmon: Run your fingers over the salmon to check for any bones. If you feel any, remove them carefully using fish tweezers or pliers. Cut the side of salmon in half so you have two equal-sized pieces.
Apply the cure: Place the salmon pieces skin-side down. Evenly rub the cure over all the exposed flesh, ensuring it is fully covered.
Assemble and wrap: Sandwich the two pieces together, flesh side to flesh side. Wrap tightly in cling film, then use a cocktail stick to poke a few small holes to allow excess liquid to escape.
Weight and refrigerate: Place the wrapped salmon in a deep tray to catch any liquid released during curing. Put another tray or board on top and weigh it down (a few tins of beans work perfectly).
Cure the salmon: Refrigerate for 48–72 hours, turning the salmon every 12 hours for an even cure.For a firmer texture, cure for 72 hoursFor a softer texture, cure for 48 hours Rinse and dry: Once cured, remove the salmon from the fridge. Unwrap and scrape off the cure mixture, then rinse briefly under cold water to remove any remaining cure. Pat completely dry with kitchen paper.
Finish with dill and lemon: Finely chop the remaining dill (20g) and zest the final lemon. Sprinkle evenly over the cured salmon.
Slice and serve: Using a very sharp knife, slice the gravlax thinly on the diagonal. Serve immediately or store in the fridge until ready to enjoy.