Blend the sambal ingredients together and set aside.
Blend the chutney ingredients coarsely and set aside.
Heat a heavy saucepan with the oil. Blend the onion, garlic, ginger and chillies then add to the oil and fry gently for two to three minutes until soft. Add the curry powder and cook for one minute more.
Add the potatoes, coriander stems and tamarind, stir well and pour in the coconut milk. Bring to the boil and simmer for 15 minutes.
Garnish with the coriander leaves and serve with the sambal and chutney, and some pappadums if you like