Heat ghee or shortening in thick-bottomed pot until shimmering
Add cinnamon, cardamom, cloves, bay leaf and fennel and stir for 2 minutes or so, until fragrant
Add curry leaves, chillies, onion, turmeric, garlic/ginger paste and stir for another 2-3 minutes
Add remaining spice powders, vinegar and sugar. Stir and deglaze
Add lamb, 1 tsp salt. Mix well until entirely coated.
Cover and reduce heat. Allow to cook slowly, stirring occasionally, for 20 minutes.
Add potatoes and stir well.
Cover again and cook slowly for 40 minutes, stirring occasionally. Add water if the mixture gets too dry.
Pour in diced tomatoes, liquid and all. Cover and cook for another 20 minutes.
Once the potatoes soften completely and their starch thickens the curry, stir in the chopped cilantro.
Serve immediately, over rice or in a hollowed out loaf of bread. Serve with Kachumber salad or carrot sambals as a side and garnish with achar.