Soak 10-12 red chillies in warm water overnight. De-seed them as per how hot you want the masala.
To prepare the vindaloo masala, first grind together cumin seeds, coriander seeds, fenugreek seeds, peppercorns, cloves, green cardamoms, and cinnamon.
Next, add in the soaked red chillies, ginger, and garlic. Grind it into a paste. Finally, add in the vinegar and blend it into a fine paste.
Take the curry-cut chicken in a large bowl. Add the vindaloo masala, salt, turmeric powder, and tamarind pulp. Mix well and keep aside.
Heat 2 tbsp of oil in a pan. Add in the finely chopped onions and saute until translucent.
Add in the marinated chicken and sear on high heat.
Add in about half a cup of water, reduce the heat, cover with a lid, and let it simmer until the chicken is cooked. Keep stirring occasionally.
Adjust the gravy. Check the salt and add more if required.
Chicken Vindaloo is ready to serve.