Combine onion, ginger, garlic, mustard seeds, cumin seeds, cinnamon stick, peppercorns, and cloves with vinegar in a blender or food processor and grind into a thick paste.

In a large bowl, mix the remaining vinegar and water.

Add pork cubes to the bowl and thoroughly rinse with the vinegar mixture; drain.

Pat the pork dry with paper towels.

In a clean bowl, mix the paste and pork cubes, ensuring the pork is fully coated.

Cover the bowl with plastic wrap and marinate in the refrigerator for 8 hours to overnight.

Heat vegetable oil in a large skillet over medium-high heat.

Fry curry leaves in the hot oil until golden brown, about 2 to 3 minutes.

Add the marinated pork, tomatoes, and turmeric to the skillet.

Cook and stir until the tomatoes are completely softened, about 10 minutes.

Season the pork mixture with salt.

Pour enough pork stock over the mixture to ensure everything is at least half-submerged.

Bring the stock to a simmer, cover the skillet, and reduce heat to medium-low.

Simmer until the pork is completely tender, about 1 to 2 hours.

Remove the lid from the skillet and continue to simmer until the sauce is very thick, about 10 minutes.

Garnish with cilantro.