Add vinegar and 1/4 cup sugar to the pan, then cook for 2-3 minutes until the mixture starts to caramelize. Add stock, ginger, garlic, and fish sauce, then bring to the boil. Reduce heat to medium-high and simmer for 3-4 minutes until sticky and reduced. Return pork cutlets to the pan and cook, turning, for 1-2 minutes until well coated in the sauce.