Peel, core, and slice the Granny Smith apples.

Peel, core, and chop the pineapple into small pieces.

Grate the zest from the lemons and reserve the juice separately.

In a large, heavy-based saucepan, combine the prepared apples, pineapple, lemon zest, and lemon juice.

Simmer the mixture gently for approximately 15 minutes, or until the fruit becomes tender.

Add the caster sugar to the fruit mixture, stirring continuously until the sugar is completely dissolved.

Increase the heat and bring the mixture to a rapid boil for about 15 minutes, or until the jam reaches its setting point.

Carefully spoon the hot jam into sterilized jars.

Cover the jars immediately to seal.

Store the sealed jars in a cool, dark place for up to 3-4 months.

Ensure all storage jars are thoroughly sterilized before use.