Add whole black peppercorns to a mortar and pestle and grind to make a coarse powder. Set aside.
Heat oil in a pan over medium-high heat.
Once the oil is hot, add mustard seeds, chana dal, and urad dal, and cook until they turn slightly brown (30-40 seconds), stirring frequently.
Add curry leaves and asafetida and let them crackle for 3-4 seconds.
Add onions and cashew nuts to the pan and fry until they turn slightly brown (1-2 minutes). Stir frequently while frying.
Now add cooked and cooled rice, ground pepper, and salt and mix well.
Cook for 2-3 minutes. Check for salt and add more if needed. Serve hot.
Video
Notes
If you are making it with fresh rice, cool it down fully. The best way to cool down freshly cooked rice faster is to spread it on a baking tray and cover it with cling film. Then refrigerate for 30 minutes or freeze for 15 minutes.You can skip adding onions to make no onion, no, garlic, pepper rice.