1. Halve the mandarins and carefully remove all the pips. Chop the flesh and peel quite finely, removing any further pips. Peel, core and slice the apples.
2. Mix the apple peelings and core with pips from the mandarins and tie them securely in a piece of clean muslin.
3. Put all the chopped fruit in a large saucepan and pour in the water. Add the muslin package and bring to the boil.
4. Cover the pan, reduce the heat and simmer the mixture gently for 1 hour or until the fruit is soft.
5. Allow to cool until the muslin can be handled, then squeeze all the juices out of it into the jam. Pour in the lemon juice and sugar and heat the jam gently, stirring continuously, until the sugar has completely dissolved. Bring it to the boil and boil hard to setting point.
6. Pour the jam into warmed pots and top each with a waxed disc, waxed side down. Allow to cool before covering the pots with lids or pieces of cellophane.