Preheat the slow cooker if necessary; see the manufacturer's instructions. Put the apples and vinegar into the slow cooker pot and pour over the boiling water. Cover with the lid and cook on high for 2–3 hours or until the apples are tender. Don't worry if the apples discolour.
Hang a jelly bag from a frame or upturned stool and set a bowl beneath it. Ladle the cooked apples and their juices into the bag and allow to drip through.
Measure the liquid and pour it into a large saucepan; for every 600 ml (1 pint) liquid add 500 g (1 lb) of sugar. Heat gently, stirring occasionally, until the sugar has dissolved, then boil rapidly for about 15 minutes until setting point is reached. Check with a jam thermometer or spoon a little of the jelly on to a saucer that has been chilled in the refrigerator. Leave for 1–2 minutes, then run a finger through the jelly. If a finger space is left and the jelly has wrinkled it is ready; if not boil for 5–10 minutes more and then retest.
Skim any scum with a slotted spoon, then stir in the chopped herbs. Leave the jelly to stand for 5 minutes.
Warm 3 clean jars in a low oven for 5 minutes. Ladle the jelly into the warm jars, cover the surface with waxed discs, add cellophane jam pot covers and secure with elastic bands. Label and store in a cool place. Once opened, store in the refrigerator. Serve with lamb.