Sprinkle the salt over the salmon fillet, then place the fish in a plastic zip-loc bag. Put the bag in the freezer and set a heavy weight on it. Leave in the freezer for 3 days.
When ready to serve, rinse the salmon briefly, then pat dry. Allow the fish to thaw slightly, as it’s easiest to slice when still slightly frozen. Slice very thin and allow to thaw completely before serving.