For the soaked bananas, peel bananas, cut into finger-thick slices and drizzle Cointreau over them. Bring the water to the boil, adding the sugar and stirring constantly to dissolve. Skim off the foam that forms and continue to boil for a few minutes.
Mix the cornflour and orange juice to a homogeneous liquid. Remove sugar water from heat source, stir in orange juice and bring to the boil again. Soak the banana pieces with the liquid.
Mix confectioners’ sugar and vanilla sugar and sprinkle on the soaked bananas.