Heat oil in a large saucepan over medium heat-high heat.
Add bay leaf, minced ginger and garlic. Sauté, stirring, for about 1 minute or until aromatic.
Add water and vegetable broth (stock).
Add dal. Stir to combine.
Cook for about 6-8 minutes or until mushy.
Remove bay leaf.
Using a stick blender, blend the soup to make silky smooth purée.
Add turmeric, cumin and red chili powder. Season with salt. Stir to combine. Simmer for about 2 minutes.
To make the tempered spices, heat 1 tablespoon oil in a frying pan. Add mustard seeds and curry leaves. Fry for a few seconds or until the mustard seeds pop. Add tempered spices to the soup. Stir.
Garnish with coriander (cilantro) leaves if you like.