Combine whole urad dal/black lentils and kidney beans in a big saucepan and rinse it thoroughly. Then add 3 cups water to it and let it rest overnight. (do not drain this water).
In a blender combine all the grinding ingredients ( onion, tomato, ginger, garlic, cumin seeds, 1 cup coconut milk) and blend it smooth.
Turn on your instant pot at sauté mode and let the inner pot warm up. Then, pour the blended masala to it. Stir nicely, and let it cook. Immediately, add cinnamon stick, asafetida and dry red chilies to it. Stir again and let it cook until it thickens and reduces (about 10-15 minutes). Keep stirring at intervals of 3-4 minutes to make sure it does not stick at the bottom. If it starts splashing then lightly cover it with the lid. Do not seal the lid at this point.
Now, add turmeric powder, chili powder, coriander powder, cumin powder, garam masala to it and sauté very nicely.
Now, stir in the soaked lentils and beans along with its water. Add another 2 ½ cups water and salt.
Turn off the instant pot and close the lid and seal the valve. Turn it on at manual high for 60 minutes. Once done, let it release the pressure on its own naturally which will take another 10 minutes.
In the meanwhile, drain the cashew nuts with the help of a sieve and combine cashew nuts and 1/2 cup coconut milk in the blender. Blend it smooth and keep it aside.
Once the lentils are cooked open the lid and stir once. Then, add in the blended cashew and mix very well.
Garnish with chopped cilantro and serve with rice, naan and onion salad.