Add the rinsed dal, water, tomato, green chilli, turmeric and salt to a pressure cooker. Cook for 3 to 4 whistles, until the dal is completely soft. Let the pressure release on its own.
Open the cooker and whisk the dal lightly with a ladle so it turns smooth and creamy. If it looks too thick, stir in a little hot water — dal tadka should pour easily, like a thick soup. Keep it on a gentle simmer.
For the masala, heat 2 tablespoons ghee in a pan on medium heat. Add the cumin seeds and let them crackle.
Add the chopped onion and fry, stirring often, until it turns golden brown at the edges — about 6 to 7 minutes. This browning gives the dal its restaurant flavour, so do not rush it.
Add the ginger-garlic paste and fry for a minute, until the raw smell goes away.
Lower the heat, add red chilli powder, coriander powder and garam masala, and stir for a few seconds.
Pour the cooked dal into the masala. Mix well and simmer for 4 to 5 minutes so the flavours come together. Check the salt and adjust.
For the final tadka, heat 1 tablespoon ghee in a small tadka pan until it is quite hot. Add the cumin seeds, sliced garlic, dried red chillies and asafoetida. Fry until the garlic turns light golden — not brown.
Take the pan off the heat, stir in the Kashmiri chilli powder, and immediately pour the sizzling tadka over the dal. Cover the dal for a minute so it absorbs the smoky aroma.
Garnish with fresh coriander and serve hot with jeera rice, plain basmati, naan or roti, plus a lemon wedge on the side.