3 large leeks, cut into small rings and rinsed in cold water till clean
4 Tbsp unsalted butter
1 Tbsp sugar
2 cups chicken or vegetable broth
Put the lentils in a bowl and rinse three times with cold water. Fill the bowl again with cold water, and leave the lentils to soak for 2 hours. Drain off water.
Meanwhile, make the caramelized leeks: In a skillet, sauté the chopped leeks in the butter till they start to brown, about 8 minutes.
Stir in the sugar and cook for another minute, stirring constantly.
Stir in the broth and bring to a simmer. Cook, stirring occasionally until the liquid is cooked off, about 20 minutes.
Remove skillet from the heat and set aside.
To make the dal, place a medium saucepan over medium heat. Add the butter or ghee. As it melts, add the ginger and sauté for two minutes.
Add the garlic and sauté for 1 minute. Add cumin seeds, brown mustard seeds and Turmeric Powder and cook for another 30 seconds.
Add the drained lentils and cook, stirring, for 1 minute. Add the salt, pepper, tomatoes, caramelized leeks and broth. Bring the soup to a low boil, then turn it down to a simmer. Simmer for 1 1/2 hours, stirring occasionally.
Test for salt and a bit more, if desired. Remove the pan from the heat. Transfer soup to bowls and garnish with cilantro.