Preheat the slow cooker if necessary; see the manufacturer's instructions. Cut each apple quarter in half again, then put into the slow cooker and toss with the lemon rind and juice. Arrange the apples so that they are in a single layer.
Sprinkle with the sultanas and sugar, pour over the cider and dot with the butter. Cover with the lid and cook on high for 1½–2 hours or until the apples are tender but still holding their shape.
When almost ready to serve, heat the butter for the almond granola in a frying pan, add the remaining ingredients and fry, stirring until hot and browned. Spoon the apples and the cidery juices into bowls and sprinkle hot granola on top. Serve with cream or ice cream.