1. Soak the tamarind overnight in water. Strain it and save the liquid.
2. Put tamarind, tomato paste, icing sugar, ginger/garlic paste, salt and onion into a blender and mix to a smooth puree.
3. Heat oil in a wok, add cumin and coriander seeds, mustard seeds and curry leaves, cook until the spices start popping.
4. Stir the beef cubes into the spices and fry for four minutes until the meat is brown.
5. Add chillies, all spices, tamarind mixture and reserved tamarind liquid and cook for 25 minutes.
6. Garnish with coriander leaves.