Whisk 2 cups of curd well and keep aside.
Heat oil, add cumin, mustard seeds, chana dal, urad dal, and asafoetida. Let spices crackle and lentils brown for a flavorful Dahi Tadka base
Now add 2-3 chopped green chilies, 1 tablespoon of grated ginger and fry for 1 minute. Then add 1 finely chopped onion and fry it until it becomes light golden.
Now add 2-3 whole red chilies, 1/2 teaspoon red chili powder and 1/2 teaspoon turmeric and mix well.
Turn off the gas, add whisked curd gradually, stirring constantly to prevent curdling. Add 1/4 cup water if needed to adjust the consistency of the Dahi Tadka.
Add salt to taste, sprinkle green coriander on top and serve hot tempered curd with roti or rice.