Heat oil in a pan. Add the coriander seeds, fennel seeds, cumin seeds, peppercorns, curry leaves and red chilli and saute till you get a good aroma.
Add the onion, shallots, ginger, garlic, green chilli, coriander leaves and turmeric powder and saute till the onions turn light brown in colour.
Add the tomato and saute till becomes soft and onions turn a shade darker.
Switch off heat and let cool. Once cooled, grind to a smooth, fine paste.
Add it to the mutton pieces along with salt. Cook till the mutton is done.
In another pan, heat oil. Add mustard seeds when they start to splutter, add the onions, curry leaves and red chilli.
Saute till the onions turn brown in colour. Add the cubed potatoes and saute for a minute.
Pour this into the mutton and stir well. Cook till the potatoes are done.
If you want gravy, you may add a little water. Serve hot with rice or roti.