Creamy chicken & mango curry

Name: Creamy chicken & mango curry
Prep time: 10 min
Cook time: 1 h
Total time: 1 h 10 min
Cuisine: Indian
Ingredients: 12 boneless, skinless chicken thighs; 2 tsp turmeric; 2 tbsp sunflower oil; 2 onions , 1 chopped, 1 quartered; 2 large ripe mangoes; 6 tbsp good-quality korma paste; 100g ginger , roughly chopped; 2 tsp ground cumin; 1 tbsp black onion seed (kalonji or nigella); 400g can light coconut milk; 600ml chicken stock; few coriander sprigs, basmati rice, naan bread, mango chutney, lime pickle and our sides (see 'goes well with'), to serve (optional)