Grind together the ingredients from chopped ginger & garlic - water to a smooth paste. Keep it aside.
Heat oil in a pressure cooker and add sliced onions. When it browns, add ground paste. Mix well, Add 1-2 tbsp hot water to bring together the masala. Once the oil starts appearing, add chopped tomato & salt. Mix well. When the tomato becomes soft, add cleaned mutton pieces. Stir well.
Make sure the mutton pieces are coated well with the masala. Add 1 cup hot water and mix well. Bring to a boil. Close the cooker and put the weight on. After the first whistle on full flame, reduce the flame to low-medium and cook till the mutton is done ( i keep it for 10-12 whistles).
Once the gas is switched off, keep the cooker closed till pressure drops, 10-15 mins. Open the cooker, if there is excess water, continue cooking on low-medium flame, till the gravy is almost dried and the curry reaches a semi dry consistency. Make sure you stir the curry in between, otherwise it may stick to the bottom.
Let the curry rest for 15-20 mins, before serving. Serve with Plain Rice, Ghee Rice, Veg Pulao, Roti etc;
Notes
I used coconut oil for this recipe, but the original recipes uses refined oil.The original recipe use slow cooking method. If you want to try that, the recipe suggests keeping a deep lid containing boil water to cover the dish while cooking. It says this will help the meat to cook well. You may also need to adjust the qty of water accordingly.You can store the curry in fridge for 2-3 days.If you prefer a spicier version, increase the qty of chilli powder.