Wash the dhal in several changes of water until it runs clear. If you use oily dhal soak it in hot water for a while before rinsing it several times.
Put the dhal in a medium saucepan with I l of water and bring to the boil.
Lower the heat, cover and simmer, stirring occasionally for 20-30 minutes. Add more water and check it does not stick to the bottom.
When the dhal is cooked soft enough to squash between two fingers remove from the heat and blend with a masher or blender to a smooth consistency
Return to blended dhal on low heat and add the ginger, lime juice, green chilli, curry leaves, turmeric, salt, 1/4 tsp asafoetida and the nuts if you have chosen them.
Add 200ml water adn simmer for 6-8 minutes. Add more water if necessary. Until it has the consistency of a creamy soup.