Lox, or salt-cured salmon, is a relatively new addition to Jewish cuisine. But it is the choice of fish, and not the process, that is the new part. According to Claudia Roden, fish cured in salt has long been a tradition in Sephardic communities, but the fish of choice in earlier days were tuna and mackerel.
In The Book of Jewish Food, Roden provides the following recipe from Geneviève Lehmann, a fishmonger in Sens, France. Roden notes that the important thing is to start with very fresh fish.
Cured Salmon (Lox) and Sauce
2 filets, weighing about 2 pounds 3 Tbsp coarse sea salt or kosher salt
For the Sauce:
1 cup whipping cream A good bunch (1/2-cup) of herbs - dill, chervil, or chives, or a mixture of these - finely chopped Salt and pepper
Carefully remove any small bones from the filets (tweezers will help). Sprinkle the filets with the salt, on the skin side as well as inside (the salt must be coarse, not fine, so that it draws out the moisture; fine salt is absorbed and results in too salty fish), and put them together to reform the fish. Cover with plastic wrap and leave in the refrigerator for 12 hours, turning the salmon over when juices start to collect.
Before serving, scrape off the salt and wipe with a paper towel, then rinse in cold water. Taste a piece. If it is too salty, the saltiness can be removed by soaking in fresh water for as long as necessary. Cut thin slices at an angle.
To make the sauce, whip the cream and add the herbs and salt and pepper.