I've never made this from a recipe, I received some vague directions on how to cook it once and have been making it ever since, which is why I have chosen to not write in a prescriptive recipe format.
Put some split red lentils in a saucepan with a pinch of turmeric, a few cardamom pods, a cinnamon stick and a pinch of salt. Cover with water, about twice as much water as lentils. Bring slowly to a simmer, skimming of any scum that rises to the surface. Let it cook at light simmer until the lentils have collapsed and turned to a porridge. Stir frequently during cooking, especially near the end when there is more risk of the lentils sticking to the bottom of the pot. If it looks like it is going to dry out during cooking, add a little more water, if it looks too liquid, boil it off until you have a better consistency. This really isn't precise cooking.
Heat some ghee or butter - a good spoonful- in a frying pan. When the butter/ ghee is bubbling, dd some chopped garlic and ginger, ground cumin, coriander, asfoetida and chilli to the pan and fry for about 1 minute. Tip the spice mix straight into the dal and stir in. (For 500g lentils, I use about 2tsp each ground cumin and coriander, a pinch of asfoetida and a tsp chilli powder.) Season the dahl with salt and garam masala, and a squeeze of lime juice. Eat with rice or indian bread, or as part of a larger Indian meal.