Firstly in a large bowl mix all the ingredients under marination. Now marinate for atleast 1 to 2 hours or over night.
In a mixer grinder place the ginger, garlic and 1/2 of 1 onion and make fine paste. Keep it aside.
Precook the meat: Place the marinated mutton/lamb in the pressure cooker along with 1 cup of water and pressure cook for 4-5 whistles. the meat should be until the almost 90% done. Set aside the pre cooked meat and the marinade and sauce.
Add 3 tbsp of mustard oil in a pan and heat it on medium to high flame to burning point. Then reduce the heat and add the potatoes and fry until golden brown. Drain and keep it aside.
Add the rest of the oil and heat it to burning point. Then reduce the heat and add dried red chillies, bay leaves and panch phoron (Indian five spice). Then add the sugar and stir it around until it starts to dissolve and looks slightly caramelised (make sure not to burn the sugar). Caramelised sugar add a lovely vibrant shade to the dish.
Now add the sliced onions and and fry it on medium to high heat until the onions are soft golden brown in colour.
Then add the ginger-garlic-onion paste to the onions and continue frying until the raw smell disappears.
Add the turmeric powder and chilli powder and sauté for 1 to 2 minutes.
Now precooked meat (not he sauce) to the onions. Toss the motton/lamb well with the onion mix. cook for 4-5 minutes until the meat and the onion blends together.
Now add the fried potatoes to the meat and mix everything well.
Slowly start adding the cooking liquid (from the precooked meat) to the meat and potato mixture and the tomato and continue to cook on medium heat.
Cover and cook slowly adding the cooking liquid a little at a time. This will take almost 35-40 minutes to cook the meat and the potatoes with the spice mix and infuse the flavours.
Finally add the freshly ground garam masala in to the meat and toss everything well. Check the seasoning, add salt if required. I did not add more water in this curry, but if you like a little more gravy add a cup of water and continue cooking until it reached the desired consistency.
Sprinkle with freshly chopped coriander and serve it hot with rice or pooris.