In a pan, on very low heat, put the butter, sugar, cinnamon and 1 tbsp rum. Leave everything to mix well into a syrup.
Peel the bananas and fry them in this mixture for 10 minutes; at the halfway point turn them over carefully. Pour the remaining rum over them and flambe.
If you're fast enough, you can try serving bananas while they're still flaming. You can flambe the bananas whole or cut into pieces.
If whole, you have to be very careful not to break them apart.