This curry is great on its own or as an accompaniment. It is not too hot or spicy, just right! If you want it hotter, just add more chilli. I prefer to use all fresh ingredients and grind them myself as they are more fragrant but using prepared spices will be fine.
Heat the mustard seeds in a dry pan until they start to pop. Add the ghee or oil, onion, garlic and ginger; cook, stirring, until the onion is soft.
Add the turmeric, chilli powder, cumin, garam marsala and potato, and season with salt and pepper. Stir until the potato is coated with the spice mixture. Add the water and simmer, covered until the potato is just tender. Stir occasionally to stop the mixture sticking to the bottom of the pan.
Add the peas and stir until well combined. Simmer, covered, for 3-5 minutes, or until the potato is cooked and all the liquid is absorbed. Stir in the mint and season with salt and freshly ground black pepper.
Serve on its own or with a beef rendang or chicken korma - lovely!