First of all clean and wash mutton pieces and leave it in colander for 10 minutes to drain out excess water.
Now in a mixing bowl, take all the ingredients listed under marination category, mix all of them together and add mutton pieces to this marinade.
Mix the lamb pieces well in marinade and leave it for at least 25-30 minutes.
Now, in a pan dry roast Red chillies, mustard seeds, fenugreek seeds, cumin seeds, fennel seeds, onion seeds for 5-6 minutes.
Cool slightly and then grind coarsely with the help of a pestle & mortar.
Take a blender, and puree tomatoes, with green chillies and ginger.
Heat mustard oil in a thick-bottomed pan until you see smoke coming out of it, cool it and then heat it again.
Now, add chopped onions and sauté till brown. After this, add coarsely ground masala powder and saute it for one minute.
Now add marinated mutton, cook on high heat till mutton pieces are well browned.
At this stage, add tomato puree and cook this until it starts leaving oil . Then add two cups of water and cover the pan with lid.
Lower down the flame to medium heat and cook till the mutton is properly cooked while stirring and checking the tenderness occasionally.
Once its cooked properly, switch off the flame and garnish with coriander leaves. Enjoy it with Rumali Roti / Naan / Rice of your choice.