Despite the popularity of Indian cuisine, its complexity and variety of the spices used can often be quite intimidating. One of the most important things we learned while spending time in New Delhi was that the amount of spices used in a curry is far less than we had anticipated. The level of heat in the curries we tried was complex rather than hot. The spices that were used were so well balanced and gave everything a fragrance.
Pat the lamb dry with paper towels to remove excess moisture, and season generously.
Heat the vegetable oil in a large pot over a high heat. Brown the meat in batches and set aside.
Reduce the heat and to the same pot add the onions. Season and cook for 8 minutes or until the onions are very soft. Do not brown.
Add the dried spices and cook for 3 minutes or until spices become very fragrant. Add the vinegar and cook for a further 5 minutes.
Add the lamb and any juices back to the pot. In a small food processor, whiz together all ingredients for the paste until well combined. Add to the pot. Cook for 5 minutes.
Add the rest of the ingredients and bring to the boil, then reduce the heat to a simmer and cook for 90 minutes–2 hours or until the meat is tender and the sauce has thickened.
Stir occasionally to make sure it doesn't stick on the bottom. Taste and season again just before serving.