Use only very ripe bananas, full of sugar (black) spots, and mash them with a fork; they will liquefy too much if you use a blender or a food processor.
Cream the butter with 5tablespoons of the sugar, then add 2 tablespoons of the rum and continue beating until fluffy. Peel and mash 3 of the bananas with 1 tablespoon of the lemon juice. Grate the chocolate into the banana puree. Blend the banana puree into the creamed butter. Whip the cream until