Heat 40.5 g vegetable oil in a heavy non-stick saucepan over medium heat.
Add the whole spices for the oil (2 g carom seed and 0.3 g asafoetida) and wait until they sizzle.
Stir in the ground spices for the beans (2.6 g kashmiri chilli powder and 3 g ground turmeric), then add 470 g butter bean and stir for 2–3 minutes.
Pour in 398 g water, add 10.8 g jaggery and salt to taste, cover, and cook on low for 25 minutes, stirring once halfway, until the beans begin to soften.
Add 12 g tamarind paste and stir; press some of the beans against the pan with the spoon to thicken the curry, then mix well.
Scatter the coriander garnish to taste over the top.
Steep a tiny pinch (0.1 g per 2 g turmeric) in 2 tbsp warm water; use to match the rich golden hue. Contributes an aristocratic, honeyed floral flavour rather than earthy bitterness.
Use 80% of the weight. Granulated sugar is sweeter by weight, but gives a cleaner, one-dimensional sweetness that lacks jaggery's caramel, molasses depth.
Soak and blend into a paste; use 100% to 120% of the weight. Adds rich, natural, fruity sweetness with complex, dark molasses notes that thicken the gravy.