Place the lentils in a sieve and wash well under cold running water. Drain and place in a large saucepan with 850 ml (1 1/2 pints) 3 1/2 cups of the vegetable stock, the carrots, onions, tomatoes and garlic. Bring the mixture to the boil, reduce the heat, cover and simmer for 30 minutes.

Meanwhile, heat the ghee or oil in a small pan, add the cumin, coriander, chilli and turmeric and fry gently for 1 minute.

Remove from the heat and stir in the lemon juice and salt to taste.

Puree the soup in batches in a blender or food processor. Return the

soup to the saucepan, add the spice mixture and the remaining 300 ml (1/2 pint) 1 1/4 cups stock or water and simmer for 10 minutes.

Add the milk to the soup and adjust the seasoning according to taste.

Stir in the chopped coriander (cilantro) and reheat gently. Serve hot, with a swirl of yogurt.