take 1 cup arhar dal/tuvar dal/pigeon pea lentils in a bowl or colander. rinse a couple of times and add the rinsed dal in a pressure cooker.
add sliced onions, chopped tomatoes, green chilies (sliced, slit or chopped), turmeric powder, red chilli powder and a generous pinch of asafoetida. pour 2 cups water. mix well.
pressure cook the dal for 8 to 9 whistles or 14 to 15 minutes. when the pressure comes down on its own, in the cooker, check the dal. the lentils have to be cooked very well and become soft and mushy. with a spoon lightly mash the dal mixture.
add 1 cup water to the dal. you can add water as required depending on the consistency you want. for a thicker dal, add less water and for a thin dal, add slightly more water. stir very well. season with salt as per taste.
keep the dal on stove top and simmer for some minutes till you get the desired consistency. do stir the dal at intervals so that the dal does not get browned or burnt from the base. cover and keep aside.
in a small pan or tadka pan, heat 2 tbsp ghee or oil. add 1 tsp mustard seeds.
let the mustard seeds crackle. then add 1 tsp cumin seeds.
saute the cumin seeds till they change color and splutter. this takes a few seconds.
add 4 to 5 medium garlic cloves, crushed lightly with peels. you can also slice or chop the garlic. saute for half a minute.
add 1 to 2 dry red chilies (broken and deseeded), 9 to 10 curry leaves. saute till the red chilies change color and the curry leaves become crisp.
pour the entire tempering mixture in the dal. cover and allow the tempering flavors to infuse with the dal.
lastly add chopped coriander leaves.
stir and serve home style dal tadka with steamed rice or chapatis.