Rinse lentils in a strainer using cold water. Pick-over and discard any bad looking lentils. Then place them in a bowl and cover with cold water to soak for half an hour (or overnight). Drain in the strainer and set aside.
Heat the oil in a large frypan over a medium heat. Add half the mustard seeds and half the cumin seeds. Stir for 1 to 2 minutes until they start popping.
Add the garlic, ginger, curry leaves and half the onion. Stir until soft- about 8 minutes.
Add the tomato, cashews, turmeric, garam marsala, ground chilli, ground coriander and the vegetable stock. Stir occasionally until thick - roughly 5 minutes.
Add lentils and enough water to cover the lentils (about 1.5 litres). Bring to the boil and then reduce heat to low. Stir occasionally until the lentils are cooked through and tender - about ½ hour.
In a separate pan, heat the oil and add the remaining spices. Stir for a couple of minutes, until fragrant. Add the remaining onion and stir until the onion is golden.
Combine the onion mix with the lentil mix.
Season with salt and pepper.
To serve sprinkle chopped coriander over the top use watery consistency for dal soup.
If your into pressure cooking do steps 1 -4, then step six. Place everything in pressure cooker.