You'll need about 10 unripe Hog Plums, the Indian type.
Peel them. Use something heavy, like a mortar and pestle, to lightly smash each plum a couple of times to break them up slightly. This makes it easier for the juice to come out. These plums are hard to cut because of the pit, so smashing them helps.
Next, heat 1 tablespoon of mustard oil in a pan.
Add either 1 teaspoon of mustard seeds or 1 teaspoon of Bengali five-spice as tempering. Either one is fine, but mustard seeds are preferred.
Toss in a dried red chili too.
Then, add the smashed plums, followed by 1 teaspoon of salt and ½ teaspoon of turmeric powder.
Cook for 5 minutes, stirring occasionally.
After that, add about 500ml of water and let the plums cook on low heat for at least 20 minutes. The longer they cook, the more juice they'll release.
After 20 minutes, add 10 tablespoons of sugar or 150g of jaggery and mix well.
Cook for 5 more minutes, then turn off the heat. The Amra-r Ambol should be somewhat liquidy.
Add more water if it's too thick. Let it sit at room temperature before you eat it. For the best taste, you can also keep Dishi Amrar Ambol in the fridge.