Peel and dice the potatoes into 1cm (½ inch) cubes.
Place a wok on a high heat, then add the following ingredients in this order: 200ml (7fl oz/¾ cup plus 2 tbsp) hot kettle water, oil, brown mustard seeds, cumin seeds, diced potatoes, turmeric, chilli powder, garlic powder, ginger, tamarind paste, soft brown sugar and salt t