Heat oil in a pan until hot. Add in the mustard seeds, urad dal, cumin seeds, dried red chilli and curry leaves. Let the mustard seeds splutter. Add in the finely chopped garlic and onions. Fry till soft and translucent. Add in the washed, peeled and diced potatoes. Add in the salt, sambar powder, asafoetida and turmeric. Stir well to combine.
Add in half a cup of water, cover the pan with a lid and simmer for 10 minutes on low flame. After 10 minutes, remove the cover and saute the potatoes for 15-20 minutes until nicely brown and roasted. Keep tossing every couple of minutes. Let the flame be low at all times. After 20 minutes, the potatoes should be nicely roasted and brown. Remove off heat and serve with rice.