There are so many varieties of chillies in India, and indeed here on our doorstep, that it is often difficult to know which ones to use when and how hot they are once cooked. The general rule is the smaller they are, the hotter they are. Most supermarkets now sell these large, fat green chillies which are ideal for stuffing. If using jalapenos, try to find large ones as the stuffing takes away from the heat, as does the yoghurt. It might seem like a complicated dish but it is really easy, just with many components.