Soften 50 g butter over low heat (or microwave) then beat with a wooden (or plastic) spoon, until thickened creamy. Well crushed bananas with a fork, sprinkle with sugar, flavored with rum and add the mixture to the butter. Spread in appropriate glasses or bowls. Separately melting chocolate in 1/4 cup water over low heat, add 25 g butter, stir well and poured over the banana mixture. Decorate with nuts.