Step 1: Marinate the Chicken — Whisk the vinegar with the ginger garlic paste, cumin, coriander, turmeric, garam masala, salt, cinnamon, and cloves. Add the chicken and toss until coated. Cover and refrigerate for at least 30 minutes — 2 hours if you have time.

Step 2: Make the Vindaloo Spice Paste — Drain the soaked Kashmiri red chillies (reserve a splash of the soaking water). Blend the chillies with a few tablespoons of water into a smooth, thick paste.

Step 3: Temper the Spices and Brown the Base — Heat 1 tablespoon of oil in a large, heavy pot over medium heat. Add the mustard seeds and cumin seeds; when they pop (about 30 seconds), add the chopped onion. Cook 8–10 minutes until deep golden brown.

Step 4: Add the Chilli Paste and Chicken — Stir the Kashmiri chilli paste into the onions and fry 2–3 minutes until the oil begins to separate. Add the marinated chicken with all its marinade and sear 5–6 minutes, turning, until lightly browned.

Step 5: Simmer with Potatoes — Add the potato cubes, tamarind water, and 1½ cups hot water. Bring to a boil, then reduce to a gentle simmer. Cover and cook 30–35 minutes until the chicken is tender, the potatoes soft, and the gravy thick and glossy. If too thin, simmer uncovered for the last 10 minutes.

Step 6: Finish and Rest — Taste and adjust: salt as needed, the optional sugar if the tang feels sharp, or a splash of vinegar for more punch. Rest off the heat for 10 minutes. Garnish with cilantro and serve hot.