1. Heat oil, braise onion with Jeeru (Cumin) and taj until lightly golden. 2. Add masala and spices, then add steak, mustard and vinegar. 3. Cook till no water remains. 4. Add tomatoes and potatoes, cook until potatoes and steak are tender, adding water if needed. 5. Remove taj pieces, add sauce and allow to thicken. 6. Cool completely. Add dhania (coriander) and mix in.
Note: use filling in buns, sandwiches, pies, cigars etc. The potatoes can be omitted if you wish.