Choose ripe apples, peel them and cut into four, discarding the core and pips. Put them to cook in a covered saucepan over a moderate heat for 45 minutes, stirring occasionally. Take off the lid, add 100 g (3½oz) sugar and continue to cook, stirring with a wooden spoon, until the apples are thick enough to stand up in a mound. Take off the heat and purée through a sieve.