Boil the potatoes in a pan of salted water for eight minutes until just tender, then drain well. Heat the oil in a heavy-based saucepan or karahi over a medium-high heat, add the potatoes and fry for five minutes, or until golden-brown. Add the turmeric and fry for 30 seconds. Remove from the heat.
For the sauce, heat the oil in another pan over a medium-high heat. Add the bay leaves and fry for one minute, then add the asafoetida and stir. Add the onion and fry for five minutes; then add the garlic and ginger and fry for five minutes, or until softened and lightly golden-brown.
Add the chilli powder, cumin, coriander, amchur, turmeric and salt and fry for one minute, then add the tomato passata, green chillies and 100ml/3½fl oz water and stir together. Add the fried potatoes, reduce the heat to medium, cover the pan and cook for 10 minutes, adding a splash of water if anything catches on the bottom of the pan.
Add the peas and garam masala and cook uncovered for 3-4 minutes, or until the peas are cooked. Garnish with fresh coriander and serve.