Place a cast iron or heavy-bottomed stainless steel pan over medium heat. Add salt. Stir until heated through, about 1 minute. Pour salt into a mortar. Add sesame seeds to the pan. Stir constantly with a wooden spoon or spatula until seeds are fragrant and starting to crack. Test if the seeds are ready using the back of a stainless steel spoon; they will be dry, not wet.
Pour the toasted seeds into the mortar. Allow to cool slightly. Place the mortar at hip level, preferably while seated. Grind with a pestle until the seeds have opened and the salt pulverizes; the finished mixture should resemble rough sand.
