If you are organised then soak the dal overnight or for a few hours.
Wash the dal then pour into a large pan. To this add 5 cups of water along with a chopped medjool date. Bring to the boil then turn down the heat and simmer for 30-45 minutes, until the dal is soft. Skim off the skum as it forms on the top.
Meanwhile add the mustard seeds to a pan and dry fry until the seeds change colour and smell fragrant. Grind with a pestle and mortar.
Once the dal is cooked, blend using a hand blender. Add the rest of the ingredients (including the toasted mustard seeds) and simmer for about 15 minutes to allow the spices to infuse the dal. If the dal becomes too dry, add some more water.