Braised lamb with sweet potatoes and haricot beans

Name: Braised lamb with sweet potatoes and haricot beans
Ingredients: 2 tbsp sunflower oil; 1kg/2lb 4oz lamb neck fillet, diced; 2 large onions, sliced; 4 celery sticks, sliced; 1 garlic clove, crushed; 1 tbsp ground cumin; 1 tbsp medium curry powder; 450ml/16fl oz lamb or beef stock; 400g tin chopped tomatoes; 1 tbsp sun-dried tomato purée or paste; 2 tbsp mango chutney; 400g tin haricot beans, drained and rinsed; 2 sweet potatoes, peeled and sliced into 2cm/¾in cubes; salt and freshly ground black pepper