Add the water, lemon juice and sugar to a medium pot. Cook over medium-high heat for a few minutes, stirring all the time to dissolve the sugar. Add the apples, cover and bring to a boil.

Reduce heat to medium-low and continue cooking until the apples are soft (about 15 minutes). Uncover and cook for a few minutes, stirring occasionally. Use a masher to purée the apples into a soft mousse.

Pour into a sterilised preserving jar and close tightly, or transfer to a bowl and let cool before serving.