Mix the mascarpone with 3 tablespoons of sugar. Peel the bananas, cut them into slices and fry them briefly in the melted butter. Sprinkle with the rest of the sugar. Remove the pan from the heat, pour off the lemon and banana juice and mix.
Place 3 ladyfingers on each plate. Arrange the banana ragout and mascarpone cream on top, dust with cocoa powder.