Peel onion and chop finely. Clean the leek and cut into rings. Peel, quarter and core the apples. Cut the quarters into thin slices and drizzle with lemon juice.
Heat the oil and fry the meat in it. Season with salt and pepper and take out first. Now put the onion cubes in the pan and fry until translucent. Add apple slices and leek rings and fry for approx. 3 minutes. Add the meat again and deglaze with the stock and balsamic vinegar. Season with a little sugar and stew for 10 minutes.