In a small heatproof bowl, sprinkle the gelatine over the cold water and leave for 5 minutes until spongy. Set the bowl over a small saucepan with simmering water and stir until the gelatine dissolves. Set aside to cool.

In the same time, beat the heavy cream and the powder sugar until peaks form. Add the cooled gelatine and beat until only combined. Fold in the mashed bananas until combined.

Split the chocolate sponge cake horizontally. Set the base of the cake in a 23cm spring form cake ring. Arrange sliced bananas over the top , pour over the cream filling and smooth the top with a spatula. Cover with the domed half of the sponge cake making sure to put it right in the center leaving ¼ inch in the edges. Arrange the rest of the sliced bananas all around the edge, inserting them in the empty spaces between the ring and the filling. Chill for 3-4 hours

Sift icing sugar over the top and use the melted chocolate to decorate the sliced bananas in the edges. Best served at the same day.