Beef Tagine with Sweet Potato

1kg braising steak, cubed
1/2 tsp tumeric
1 large onion, chopped
1 green chilli, seeded and chopped
1 1/2 tsp paprika
Pinch cayenne pepper
1/2 tsp ground cumin
500g sweet potato, peeled and sliced
1 tbsp fresh parsley, chopped1 tbsp fresh coriander, chopped
1 tbsp butter
Salt and pepper

Place the beef in a large bowl, bake at 220 degrees centigrade for 30 minutes. Add the onion, chilli, tumeric, cayenne and cumin, season with salt and pepper. Add enough water to cover the meat, cover well with foil and bake for 2 hours at 180 degrees centigrade. Meanwhile, put the sweet potatoes in a pan of water, bring to the boil and simmer until the potatoes are soft. Drain well. Remove the beef from the oven, stir in the parsley and coriander. Arrange the sweet potato on top, dot with butter and return to the oven, bake until the sweet potatoes are brown.