Coat 500 g lamb with 6.8 g mustard oil and the marinade spice in a bowl. Cover and leave to chill in the fridge for 30 minutes.
Whisk the sauce spices together with 1.5 litres of water in a bowl until completely combined.
Heat 13.5 g mustard oil in a heavy-based pot over high heat. Tip in the sauce spices mixture and stir-fry for roughly 30 seconds until the oil separates out. Mix in 36 g green chilli, turn the heat down to low, cover, and simmer for 10 to 12 minutes.
Transfer the marinated meat into the sauce, replace the lid, and simmer gently for about 30 minutes until roughly three-quarters cooked through.
Pour a shallow layer of extra mustard oil into a frying pan over medium heat. Fry 250 g potato for 15 to 20 minutes until golden brown, then add them to the lamb pot along with 4.2 g granulated sugar and salt to taste. Cover and cook for another 30 to 45 minutes until the lamb is fully tender.
Melt 26.4 g ghee in a small pan set over medium-low heat. Stir-fry 87.5 g fresh coconut for 1 to 2 minutes until toasted golden, then drop in the tempering spice and fry for 1 minute until it crackles. Pour the hot tempering directly into the stew, cover immediately to lock in the aroma, and remove from the heat.
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 50% of the weight and stir in near the end of cooking. Adds warmth and depth since it contains ground coriander, but introduces stronger spices like clove and cinnamon.
Use 120% of the weight; melt gently over low heat to avoid burning the milk solids, which will yield a softer, creamier richness rather than a nutty aroma.
Use 50% to 60% of the weight, soaked in equal parts warm water for 15 minutes before grinding. Works well for chutneys, though texture is slightly finer and sweeter.
Use 1.2 times the weight in curries. Adds creamy richness and authentic flavour, but makes gravies smoother and eliminates the grated, chewy mouthfeel.