Fill a large mug with lentils (yellow split mung dhal, small orange lentils or white urad lentils). Empty the lentils into a strainer and rinse very well. You should keep rinsing the lentils until the water runs clear.
Warm a bit of oil, butter or ghee in a large saucepan and add the lentils. Cover with at least 1L of water, a pinch of turmeric and a sprinkling of sea salt. Bring to a boil and then turn down the heat allowing to simmer, uncovered, for about 30 minutes. Stir regularly and don’t be shy to add a few splashes of extra water as the lentils cook and the water absorbs. You want the lentils to get tender and the dhal to be smooth and creamy.
While the lentils are simmering, make the tarka, or tempering.
Begin by dry frying some cumin fennel and black mustard seeds (or any combination of assorted Indian spices in seed-form) in a frying pan.
Heat some rapeseed oil, ghee or butter and heat over medium-high heat. When the oil is hot add about 3-4 large banana shallots, or a couple medium sized red or white onions finely sliced. Cook for around 5 minutes.
Add 2 tiny hot chillies, sliced or whole and 2-3 large cloves of garlic, crushed or minced and some ginger if you want. Stir and cook for another 5 minutes, until the shallots brown and caramelise (you might need to add a bit of oil during this process--lower the heat if the onions begin to burn.
If the dhal is too thick, add a bit of hot water and stir and simmer for a few moments. Then, tip the onion tarka into the dhal, reserving about ¼ of it, and stir it in well.
Serve up with the reserved onions scattered on top, fresh coriander, lime wedges, yoghurt, basmati rice or rotis.