In a large pot, add lentils and hot water and bring to the boil. Reduce heat then cover and simmer for around 20 minutes or until lentils are tender.
Meanwhile, in a frying pan over medium heat, add half of the ghee and heat until melted. Add half of the cumin seeds and cook, stirring regularly, until seeds are popping.
Add half of the asafoetida and stir to dissolve. Add garlic and ginger and gently cook, stirring regularly, until aromatic. Take care not to burn the garlic.
Add garlic mixture and two-thirds of the turmeric to cooked lentils and stir to combine. Reduce heat and simmer until thick.
Meanwhile, temper the flavours to add to the dahl. In another frying pan over medium heat, add remaining ghee and heat until melted. Stir in remaining cumin seeds and asafoetida and cook until infused and aromatic
Add onion and chilli and cook, stirring regularly, until onion is soft and golden. Add tomato, garam masala, chilli powder and remaining turmeric. Cook, stirring regularly, until mixture is semi-dry.
Add tempering mix to cooked lentils and stir well to combine. Adjust seasoning with salt and pepper to taste.
Transfer dahl to a serving dish, garnish with coriander and serve.