Heat the butter in a large saucepan. Add the onion and cook for 10 minutes until soft. Stir in the turmeric, cumin and chilli and cook for 2 minutes then add the garlic, lentils, coconut milk and 600ml water.
Bring to the boil, cover and simmer for 40 minutes. The lentils should be soft and should have absorbed most of the liquid. For a more “soupy” consistency, add more water. Season with salt and pepper. Transfer to a warm serving dish.
Heat the oil in a small frying pan. Add the cinnamon stick, cumin seeds and poppy seeds and allow to sizzle for a few seconds then pour over the dhal.