1. Peel and cut the bananas in half lengthwise, then cut into large pieces.
2. In a non-stick pan, melt the butter. Add the bananas and brown over high heat. Add the brown sugar and let caramelize.
3. Grate the zest of one lime. Squeeze the two limes. Pour the juice and rum over the bananas, and continue cooking for 2 minutes, shaking the pan, until the alcohol evaporates and the sauce reaches a syrupy consistency. Add the zest.
4. Arrange the bananas delicately on 4 plates. Drizzle with hot juice.