Wash the lentils well until the water runs mostly clear.
Add the lentils to a saucepan with turmeric, salt, chilli powder and enough water to just cover the lentils.
Bring to a simmer over medium-high heat, then cover and cook for 7–8 minutes, stirring occasionally.
Once the lentils are almost cooked, reduce the heat to medium-low and cook for another 2–3 minutes, stirring regularly.
Add a splash of water if the dhal is too thick. It should be soft and creamy, but still pourable.
Turn off the heat and keep covered.
To make the tarka, heat the mustard oil in a small skillet over medium heat.
Add the mustard seeds and let them pop.
Once they start popping, add the cumin seeds, asafoetida, ginger, garlic, dried chillies and chopped shallots.
Sauté for 3–4 minutes, stirring regularly, until the shallots and garlic are golden and slightly crispy.
Be careful not to burn the garlic, as it can turn bitter quickly.
Pour the hot tarka over the cooked lentils.
Mix through just before serving, or leave some of the tarka sitting on top for presentation.
Serve the dhal hot with steamed rice.
