Soak the herb stems in cold water to remove dirt. Spin in a salad spinner or pat dry with a clean kitchen towel.
Spread the stems on a large baking tray so they have room. Put in a warm oven after you have finished baking something and the oven is off but still warm. Or bake them at 280°F for 30 - 60 minutes to dry completely until they feel crispy like straw.
Crush the dried stems with your hands, then crush them in a mortar and pestle or spice grinder. You can also place them in a small ziplock bag on a cutting board and roll over them with a rolling pin until they become a fine, powdery texture similar to a spice. Funnel the crushed herbs into a salt shaker, spice jar or small jar.
Add salt, about 1/2 the amount of the crushed herbs.
Shake to combine. Use the herb salt. Use it on anything like poached eggs, avocado toast, salads, fish, etc.