Put amla in blender jar with 1½ cups water in which amla was boiled and blend into a smooth puree.
Heat 1 cup water in a deep non stick pan. Add amla puree and stir. Add sugar and mix. Cook till it comes to a boil.
Mix rock salt and cumin powder in a bowl. Add 2-3 tsps water and mix. Add this to the pan and mix. Cook for 10 minutes, removing scum in between.
Pour into sterilized bottles and store.