Preheat the oven to 170C Fan. Grease and line a baking tray or roasting tin.
Put the chopped chocolate and unsalted butter in a large bowl. Set the bowl over a pot of barely simmering water and allow the chocolate and butter to melt slowly. Stir with a wooden spoon until smooth and set aside.
Blitz the bananas, sugar, milk, eggs and vanilla paste in a food processor or mini chopper until smooth. Stir the purée into the chocolate until fully combined.
Sift the flour, cocoa powder and salt over the bowl of the banana chocolate mix and then stir it in with a whisk, mixing gently until you have a glossy batter.
Transfer the batter into the prepared tin and bake for 25 minutes or until a skewer inserted in the centre comes out clean and cake is risen and firm on top. Cool on a wire rack.
When the cake is cool, you can wrap it in clingfilm and finish the rest of the cake the next day.
Trim the edges of the cake and cut it into 12 fingers, mine were approximately 3.75cm by 11cm.
Make the Chantilly cream by whipping the cream until it's firm, add the rum, vanilla and icing sugar and then whip it further until it's stiff enough to pipe.
Put the cream in a piping bag with a St Honore tip and pipe a wavy ribbon on top of the cut cake. Decorate the cakes with violas and chocolate strips, or slices of banana or grated chocolate.