Wash and clean the amla thoroughly. Boil water in a pot and boil the amla for 5 minutes to soften them. Then strain with cold water.
In a bowl, mix mustard powder, red chili powder, turmeric, rock salt, and asafoetida.
Put the boiled amla in a glass jar. Pour the prepared spice mixture over the amla and mix well.
Pour boiled, cooled water into the spiced amla and stir well to combine.
Close the jar with a lid and keep it in sunlight for 2-3 days. Stir with a wooden spoon daily. In 2-3 days, the Amla Kanji will become sour, then cool and serve.