Wash the fatback with cold water and cut it into pieces. Put about 2 finger widths of sea salt at the bottom of a small wooden barrel.
Arrange the leeks on top, cut into strips. Put the fatback, with the skin facing up and densely packed.
If there's any gaps left between the pieces, fill them with small pieces of fatback. Put slices of leeks once again and about 1/2″ (1 cm) of salt.
Continue in this same order until out of ingredients, finishing off with salt. Place a wooden lattice on top to push down and pour on boiled and then cooled water 1-2 finger widths above the fatback.
Leave in a cool area to cure. After 20 days it'll be ready for consumption.