Carrot soup

Name: Carrot soup
Prep time: 30 min
Cook time: 1 h
Total time: 1 h 30 min
Cuisine: Asian, Indian
Ingredients: 200g/7oz butter; 2 tbsp coriander seeds; 2 tbsp cumin seeds; 1 tsp dried red chilli flakes; ½ tsp ground turmeric; 1 onion, finely chopped; 2 tbsp salt; 6 garlic cloves, crushed; 1kg/2lb 4oz carrots, peeled and grated; 1 medium–large potato, peeled and grated; 2 oranges, zest and juice; 1 litre/1¾ pints vegetable stock; chilli oil, to drizzle; chopped fresh coriander leaves, to garnish