Dry roast all the spices apart from turmeric powder until fragrant. Once cooled, grind the spices with the turmeric powder and blend to a fine powder. Add the chillies, vinegar, brown sugar, garlic and ginger and blend until smooth (or if you have full faith in your blender like I do, then chuck the whole lot and grind it all with the vinegar). Add half the vinegar and grind, taste and add more vinegar as you go. If you think that the vinegar is enough, add a bit of water to grind the spices and aromatics to a fine consistency. (Refer notes)
In a nonreactive bowl, place the lamb chops and season with salt. Then add 1 heaped tbsp of the vindaloo marinade. Mix well to coat the lamb chops and marinate overnight or at least for 4-6 hours.
Allow the lamb chops to come to room temperature before cooking.
Heat oil in a large, flat pan; just as it reaches smoking hot place the lamb chops and sear on high heat for a minute. Turn over and sear the other side for another minute. Lower the heat and cook on both sides for another 2-3 minutes.
Remove the lamb chops and keep aside. In the same pan, add 1 tbsp of the vindaloo marinade and 1 tbsp tomato sauce, mix well on low heat. Taste and add more tomato sauce if necessary. After heating for a minute, add the lamb chops and mix well so that it gets evenly coated with the sauce. Allow to sit in the sauce mixture for a minute and remove.
Serve hot garnished with chopped coriander leaves.