Heat oil in a pan or pressure cooker.
Add the whole garam masalas & pieces of red chillies.
Now add the sliced onions and fry on medium heat for 10 mins till golden brown in colour.
Add the marinated mutton & sliced tomatoes.
Bhuno/Fry on medium heat for 5 mins.
Continue to fry on low heat for 10-12 mins till tomatoes are soft and pulpy.
Add 300 ml water, give a mix and pressure cook for 4 whistles till mutton is tender. Alternatively continue to cook covered in a pan for 45-60 mins till mutton is soft.
Once the mutton is soft, add the boiled potato pieces. Cook for 2 mins on low heat.
Add the coconut milk, cover and cook for 5 minutes till oil separates.
Serve with a bowl of rice.