1.Stir strawberries, watermelon, juice and sugar in a large saucepan; stand for 30 minutes or until fruit releases some of its juices.
2.Place pan with fruit mixture over high heat. Stir, without boiling, until sugar dissolves. Bring to the boil; boil, uncovered, without stirring, for 20 minutes or until jam gels when tested. (As this is a conserve, it will set slightly looser than jam.) Stir in rosewater.
3.Pour hot jam into hot sterilised jars; seal immediately. Label and date jars when cold. Store in a cool dark place; refrigerate after opening.
Try this with scones, as a sponge filling, or stirred though ice-cream. Jam-setting sugar is a special blend of sugar containing naturally occurring pectin and citric acid. It is used with fruit that is naturally low in pectin, such as berries. Jam sugar can be found in supermarkets and delis. You need approximately a 600g piece of watermelon to start with. Save the rind to make watermelon rind pickles.