Sort through the urad dal for any debris, then rinse under cool water until it runs clear.
Drain well.
In a heavy 3-quart/liter saucepan, bring the water, turmeric, and a dab of the ghee or oil to a boil over high heat.
Stir in the dal and return to a boil.
Reduce the heat to low, cover with a tight-fitting lid, and simmer gently for 30 minutes.
Add the chopped tomatoes, cover again, and continue cooking for 1 hour, or until the dal is completely soft.
Remove the pot from the heat and stir in the salt.
For the tempering (tadka), heat the remaining ghee or oil in a small pan over medium-high heat.
Add the minced ginger, cumin seeds, and broken red chili.
Fry, stirring, until the cumin seeds turn dark brown and fragrant.
Stir in the asafetida powder.
After just 1-2 seconds, immediately pour the sizzling seasonings into the cooked dal. Instantly cover the pot to trap the aromas and let the flavors infuse for 1-2 minutes.
Uncover, stir in the fresh coriander, and serve hot.
Do not skip the asafetida (hing) and red chili; they are crucial for achieving the authentic, pungent flavor profile of this Rajasthani-style dal.