Butterbean and Sweet Potato Bhuna (v)

Yes, more curry... what can I say. I like curry...

For 4 portions you need:
1/2 jar curry paste
2 jars water
2 sweet potatoes, diced
2 onions, chopped
3 cloves garlic, crushed
3 tomatoes, chopped
1 tin butterbeans, drained and rinsed
1 tbsp oil

Fry the onions in the oil, covered, for 5-10 mins till softened. Add the curry paste and cook out. Add everything else and bring to the boil. Reduce to a simmer and cook for 15-20 mins till the potatoes are tender and the sauce has reduced. Serve with roti.