Clean, wash, trim and dry pork. Cut into 1" cubes. Make Masala with onions, ginger, and tomatoes as in chicken curry, etc. Add the vinegar and Vindaloo paste and cook for 2 minutes. Add the pork and pressure cook for 20 minutes, or in a heavy pot for 1 1/2 hours, until the pieces are tender. Cube potatoes, add and cook the potato pieces coated in the liquid. Boil down the amount of water (30 minutes) while the potatoes cook.