The first step is to measure both dals in a bowl and then wash them in running water until the water runs clean.
Let the dals soak while you put a pressure cooker on the stove at medium high heat. Add dals with twice the amount of water, salt and turmeric. Close lid and steam until first whistle. Turn down heat to simmer with the lid clsoed for another 10 minutes.
Heat one tablespoon of oil in a skillet and then add cumin seeds. Followed by chillies, garlic and onion. Cook until onion and garlic are just starting to brown. Add dry spices. Cook only for a minute or two until the spices are blooming.
Finally, open the lid of the pressure cooker and add tadka to it. Mix it well and let the dal simmer on low heat, with open lid, until ready to serve. Garnish with fresh coriander.