Place the pork chops in a plastic bag. Finely chop the garlic and mince the ginger then put them in a small bowl. Add the brown sugar, vinegar, soy sauce, and mirin (or Sherry) then stir until the brown sugar is dissolved. Pour the mixture into the bag, then seal it and turn it to coat the pork chops with the marinade. Let stand 30 min at room temperature or chill in the refrigerator 3 h to overnight.