Clean and skin the salmon fillet removing any bones using your fingers or even with a pair of tweezers. You can run your hand along the salmon fillet in the opposite direction of the bones to place them. Put the salmon fillet into a dish with a rim, where it fits compactly in a single layer, keeping it in one piece, if possible, or two.
Make a mix with the salt, sugar and herbs, and sprinkle over both sides of the salmon. Pour over the lemon juice and olive oil, and grind on some black pepper.
Cover the dish with plastic wrap and refrigerate for at at least two days and up to four or five before serving. Turn the salmon over twice each day.
To serve, remove the salmon from its container. Shake off the excess liquid and put onto a cutting board. Using a long, unserrated slicing knife, start from the tail end and cut very thin slices away from you, slightly on the diagonal. Put them flat onto a large serving dish, with some overlapping, if necessary.
Whisk the remaining liquid to form a thickened oil, and spoon over the salmon. Scatter over some chopped capers if you like, a grinding of black pepper, and serve with bread or with a side salad of rocket.