4 tbsp oil
6 cloves
1 star anise
20 black peppercorns
1 3-inch cinnamon stick
2 tsp cumin seeds
6 cloves garlic
2 inch piece of ginger, peeled and grated
5 tbsp white wine vinegar
1 tbsp ground red pepper, or to taste
2 medium onions, finely sliced
1 tsp salt
1 tsp sugar
1 14oz can plum tomatoes
2 lb sweet potatoes, peeled and chopped into 1 inch chunks
yogurt to serve

Heat 1 tbsp oil, then cloves, star anise, black pepper, cinnamon, cumin. Cook 2 minutes. Grind spices. Add garlic, ginger, vinegar, and red pepper, grind into a smooth paste.
Heat the rest of the oil, add onions, cook 15 minutes until brown and caramelized, then add spices, salt, and sugar. Cook a couple minutes, add tomatoes, 8oz water. Cover, cook 5 minutes, then add sweet potatoes, simmer 20-25 minutes until potatoes are tender. Serve with yogurt.

Source: Fresh India by Meera Sodha