ATK's version of pork vindaloo

Many different iterations of this one, coconut vinegar, rice wine vinegar, cider vinegar - the constant is vinegar, and a long marination.
https://www.youtube.com/watch?v=zWlGO73xV8Q
How to Make Goan Pork Vindaloo
Or, a more UK-like expat version:
https://maunikagowardhan.co.uk/cook-in-a-curry/curry-trail-of-a-goan-pork-vindaloo/
Ingredients
(Serves 4)
600gms leg of pork cut into bite size cubes
4 tbsp vegetable oil
1 tbsp black peppercorns
2” piece of cinnamon stick
1 slit green chilli
1 tsp jaggery or brown sugar
1 tsp tamarind paste
Salt to taste
for the paste;
10-12 Kashmiri red chillies (or 5 dried red chillies deseeded if you prefer)
8 cloves of garlic
1” piece of ginger
1 tsp cumin seeds
5 tbsp malt vinegar
https://platinitwithwendy.com/blog/the-best-goan-pork-vindaloo/
Ingredients
The Meat
5 ½ Pounds (2 ½ Kgs) Pork Belly
The Marinate Paste
30 Kashmiri Chillies (Remove seeds from 15 Chillies)
2 tsp Cumin Seeds
1 tsp Peppercorns
2 tsp Turmeric Powder
20 Cloves
1/4 tsp Mustard Seeds
1 (3”) Cinnamon Stick
2” Ginger Piece
15 Garlic Cloves
1 ¼ cup Vinegar
The Cooking Process
3 tbsp Vegetable Oil
3 large Onions
Salt
½ cup Water
2 tbsp Vinegar plus 1 more tbsp
2 ½ tbsp Sugar plus 1 more tbsp
Method
Wash, pat dry and cut the pork belly into small cubes Grind the Kashmiri chillies, cumin seeds, peppercorns, turmeric powder, cloves, mustard seeds, cinnamon to a fine powder. Now add the ginger, garlic and vinegar and grind till you get a fine paste.
Apply the marinate paste to the cut pork belly making sure to cover every piece of the meat. Cover and allow it to marinate for a minimum of 4 hours. To a heated pot, pour in some vegetable oil and toss in three large onions which have been finely chopped. Sauté them till they turn translucent, about 10 minutes. Now add in the marinated meat and give it a mix. Season with salt, cover the pot with a lid, lower the heat to a medium-low and allow it to cook for about 20-30 minutes. Swirl the water in the mixer/dish that had the marinade to pick up all the leftover marinade and add it to the pot. Season with some more vinegar and sugar. Give it a mix to combine all the flavours.
Cover the pot once again with the lid on and allow it to continue cooking on a low flame for about an hour, giving it a stir occasionally. Taste the Vindaloo to see if you need to season it anymore. I added some more salt, sugar and vinegar. Cook for another 10 minutes uncovered and then take it off the heat. Vindaloo is best prepared in advance so that the flavours mature and the meat absorbs all the deliciousness.