Mix the yogurt with the curry powder in a large non-metallic bowl. Add the meat, toss to combine, season to taste and marinate in the refrigerator for 24 hours.
Heat the oil in a large nonstick wok or frying pan with a lid over a medium heat. Add the onion and stir-fry for 4–5 minutes until soft. Add the garlic and ginger, and stir-fry for a further 30 seconds.
Reduce the heat to low and add the marinated meat. Stir-fry for 10–15 minutes. Add the potatoes, tomatoes and stock and bring to the boil. Reduce the heat to very low (using a heat diffuser if possible), cover the pan tightly and simmer gently for 1½–2 hours, stirring occasionally, until the meat is meltingly tender. Check the seasoning and adjust if necessary. Serve garnished with chopped coriander.