Moong dal is optional, but it makes the dal thicker and creamier. If you use it, add a little extra water during cooking.
To save time, cook the lentils in a pressure cooker: cook for 1 to 2 whistles over medium heat, then mash them once the pressure has dropped.
You can add carrots, spinach, or fresh fenugreek leaves to the lentils during cooking.
Reserve half of the tadka to drizzle over the dal when serving.
This is a North Indian-style dal and does not contain coconut milk. For a milder South Indian-style version, stir in a little coconut milk at the end of cooking.