Heat oven to 190C/170C fan/gas 5. In a non-stick frying pan, heat 2 tsp of the oil and brown the pork fillet for 4-5 mins, turning once to cook evenly. Rub with another 1 tsp of oil and season. Transfer to a roasting tin and bake for 40 mins or until the juices run clear when you skewer the thickest part of the loin. (Timings will vary depending on thickness of the meat.)
Using the same frying pan, heat 1 tbsp oil, add the onions and cook for about 10 mins until soft. Add the apples and figs and cook for another 5 mins. Tip into a bowl and add the breadcrumbs, sage, egg, lemon zest and 2 tbsp of the chicken stock. Add seasoning, then roll into 12 balls. Put the stuffing balls on a baking tray lined with baking parchment, then bake for 20-25 mins.
When the pork is cooked, remove from the roasting tin and allow to rest for 10 mins. Deglaze the roasting tin with the remaining chicken stock, scraping any of the brown bits off the bottom, then add the vinegar, quince paste and resting juices. If your roasting tin isn’t flameproof, transfer to a saucepan and bubble down until the sauce has thickened to the consistency of double cream. Season, slice the pork and serve with stuffing, sauce and vegetables.