1. Peel the bananas and weigh the net result.
2. Dice the pineapple flesh and weigh the net result. 
3. Add an equal weight of sugar and the juice of 1 lemon.
4. Simmer everything for 30 minutes, stirring often until the sugar is entirely dissolved. The mixture should be fairly thick. 

Finishing

1. Pack into sterilized jars. 
2. Add 1 tbsp. rum to each jar before sealing. 
3. Close tightly and leave upside down until completely cool. 
4. Label and cover the jars with parchment paper.