Pressure cook the dal with 4 to 5 cups of fresh water, turmeric and a little salt for 8 to 10 whistles on medium heat, until the grains are completely soft and a few have burst. Let the pressure release naturally.

While the dal cooks, make the masala base: heat the ghee or butter in a heavy pot. Add the onion and cook on medium heat for 7 to 8 minutes until deep golden — this slow browning is the dal's backbone.

Add the ginger-garlic paste and green chillies; fry 1 minute until the raw smell goes. Add the tomato puree, red chilli powder and a pinch of salt. Cook for 6 to 8 minutes, stirring, until the masala thickens and the fat separates at the edges.

Pour in the cooked dal with all its liquid. Stir well, mashing a spoonful of grains against the side of the pot to thicken the base.

Simmer, uncovered, on the lowest heat for 25 to 30 minutes, stirring every few minutes and adding splashes of hot water as it thickens. The dal is ready when it looks like one thick, dark mass rather than grains in water. Stir in the garam masala and check the salt.

Make the finishing tempering: heat the ghee in a small pan, add the cumin and let it crackle, then the sliced garlic and fry until golden, and the dried red chilli for a few seconds.

Pour the tempering over the dal, scatter the coriander, and add the white butter if using. Serve with roti, parathas or plain rice and a wedge of onion on the side.