For the banana coconut jam, peel bananas and mash with a potato masher. Wash and dry the lemons while hot, finely grate the peel and squeeze out the juice (approx. 100 ml).
Combine bananas with rum, lemon zest and juice, and preserving sugar in a large tall saucepan. Cover and let juice steep for about 2 hours.
Heat coconut flakes with sugar over medium heat, stirring, until sugar melts and coconut flakes turn golden. Set aside and allow to cool.
Bring the banana mixture to a boil, stirring, and cook, uncovered, until slightly bubbly, 4 minutes. Stir frequently! Check for gelatinization.
Stir in coconut flakes and immediately pour into jars. Close them and turn them upside down for about 5 minutes. Makes about 1.5 kg of jam.