Spiced Cauliflower Soup

Ingredients:
1 large potato, diced
1 small cauliflower, chopped
1 onion, chopped
1 tbsp oil
1 garlic clove, crushed
1 tbsp grated fresh root ginger
2 tsp ground turmeric
1 tsp cumin seeds
1 tsp black mustard seeds
2 tsp ground coriander
1 liter vegetable stock
300ml plain yoghurt
salt and pepper
fresh coriander to garnish

1) Boil potato, cauliflower, onion, oil and 3 tbsp water and simmer covered for 10 minutes
2) Add garlic, ginger, spices and cook for 2 minutes
3) Add stock and seasoning and simmer for 20 minutes
4) Puree everything and add yoghurt