Wash the hog plums and lightly peel them. Slice around the seed (the seed is fibrous and not usually eaten).

In a small pot, combine the sliced plums and half a cup of water. Boil gently until the fruit softens and starts to break down — about 10–12 minutes. Mash lightly with a spoon.

Stir in the jaggery and let it dissolve over medium heat. Add salt, chili powder, cumin powder, and turmeric. Simmer until the mixture thickens to a jam-like consistency (another 8–10 minutes). Stir occasionally to prevent burning.

In a small pan, heat the oil. Add mustard seeds and let them pop. Optional: add curry leaves and fry a few seconds. Pour this sizzling tempering into the hot chutney. Mix well.

Let the chutney cool. It thickens further as it cools. Store in a clean glass jar — it stays good in the fridge for about a week.