Place an unopened can of condensed milk in a large roomy pan. Cover completely with cold water, and bring to the boil. Boil for two hours, always ensuring it remains completely immersed in the water. You might need to keep topping it up with boiling water as required.
Crush the digestive biscuits, and mix together with the melted butter. Line an 18cm flan tin with foil, then spread the biscuit mixture evenly over the tin. Cover and leave to cool for 2 hours.
Finely slice, and arrange the bananas over the biscuit base in a decorative pattern, topping with the caramelised condensed milk.
Decorate with whipped cream, and grated chocolate, before covering and leaving to refrigerate for a couple of hours. Serve when ready.
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