Spinach, sweet potato & lentil dhal recipe

 BBC Food's Spinach, sweet potato & lentil dhal.

Ingredients
 1 tbsp sesame oil
 1 red onion, finely chopped
 1 garlic clove, crushed
 thumb-sized piece ginger, peeled and finely chopped
 1 red chilli, finely chopped
 1½ tsp ground turmeric
 1½ tsp ground cumin
 2 sweet potatoes (about 400g/14oz), cut into even chunks
 250g red split lentils
 600ml vegetable stock
 80g bag of spinach
 4 spring onions, sliced on the diagonal, to serve
 ½ small pack of Thai basil, leaves torn, to serve