Preparation: Leave butter at room temperature to soften; peel skin of chestnut it in a blender or other to make it powdery.
Mix butter with powder sugar adding little by little chestnut powder ( mix with electric hand mixer-slower speed). And add rum.
Put the mixture in fridge for half an hour until cool down. Peel banana.
Place aluminum foil onto the table and sprinkle with little bit of powder sugar. Take the mixture from the fridge and spread to the length of banana in square shape (around 19x25cm) on aluminum foil.
Place banana in the middle and then pulling the ends of aluminum foil place all mixture around banana. Peel away aluminum foil and press well and shape the roll cake with your hands. Place roll cake onto the serving plate with baking sheet.
Chocolate glaze: Using double boiling method, melt chocolate with milk, oil and sugar. When even and melted cover roll cake from all sides. Place it in the fridge to cool down for at least half an hour. You can decorate with fresh cream if you like.