Add few spoons of water, add all the ingredients listed for the paste and grind them into a fine paste
Heat oil in a cooking vessel, add mustard seeds and as they spit, add ginger garlic paste and sauté for about 3 mts
Add coriander powder, turmeric powder and salt
Mix well
Add the chicken pieces and fry until they are vaguely browned
Take away the chicken pieces and keep aside
In the same pan drizzle some more oil and fry the onions for 5-10 miinutes until golden
Add ground masala paste and saute for 2 minutes
Add the vinegar and jaggery mixture and combine along with the chicken and its marinade and stir-fry for 5 minutes to seal the meat
Add 1 1/2 cups of water to browned chicken pieces and add in the tomatoes
Cover and simmer for 30 minutes
Remove the lid for the last 10 minutes of cooking
Cook till the chicken turns soft and it forms a thick gravy
Meanwhile, cook the potatoes in boiling water for 10-15 minutes until tender
Drain
Add the potatoes to the cooked vindaloo and serve hot
