The best method to preserve curry leaves is by freezing them along with water. This helps to preserve the color and flavor of the leaves for many months.
You just need:
2.ice cube tray
4. zip-lock bags (to store in freezer)
Collect the leaves into individual cubes in an ice tray. Add enough water to cover the leaves. Leave the tray in freezer for a few hours. Once it is frozen, remove the cubes from the tray and store in a zip-lock bag in the freezer.
If you like to add the leaves into a curry, simply toss a couple of cubes into the curry/gravy. If you like to use the curry leaves for seasoning, there are two methods, 1) simply put a couple of cubes in water for 5 min. Once the ice has melted, wipe the leaves with a towel and add into the oil, or 2) use butter instead of water for freezing. (I find freezing in butter is messy so I would recommend the first method)
You can do the same methods to preserve cilantro or any fresh herbs in kitchen
You can also use butter instead of water