Method:

1. Heat a heavy skillet to hot but not smoking, add the cumin seeds, mustard seeds, peppercorn, cardamom seeds, and cloves. Toast the seeds for 30 to 45 seconds, constantly shaking the pan to prevent burning, until the spices give off a delicious fragrance.  

2. Tip the toasted seeds into a food processor or spice grinder and blitz to create a powder. Add the chili flakes, turmeric, sugar, ginger and garlic paste and whizz again. Finally, add the tomato puree and garam masala, and blitz again. You should now have a thick, pungent paste.  

3. Place the paste into a glass bowl, add the vinegar, and stir thoroughly. Add the cubed chicken and stir to coat all the pieces evenly. Cover and leave to marinate for 30 to 45 minutes.  

4. Heat a skillet large enough to hold all the ingredients over medium heat, add the oil, and when hot, add the sliced onions and cook slowly to soften but not brown for 15 minutes. Add the chicken plus the marinade and the stock and stir well. Cook over medium heat for 30 to 40 minutes, until the chicken is cooked through and the sauce thickened. Taste and add the salt and pepper. If the vindaloo is too vinegary, add soft dark brown sugar a little at a time to your taste.  

5. Serve immediately garnished with the cilantro, and with basmati rice, mango chutney, and plain yogurt on the side.