For the toffee, place the butter and sugar into a non-stick pan over a low heat, stirring until the butter melts and the sugar dissolves.
Add the condensed milk and slowly bring to the boil, stirring continuously. As soon as the mixture thickens and begins to smell of toffee, remove from the heat and allow to cool.
For the pie, place the biscuits into a plastic bag and crush with a rolling pin. Transfer to a mixing bowl. Melt the butter in a small pan, then stir into the crushed biscuits until well combined. Press the biscuit mixture into the bottom of a 20cm/8in loose-bottomed tart tin to form the base. Chill in the fridge for 30 minutes.
Spread the toffee sauce over the biscuit base and arrange the sliced bananas over the top.
Spoon the whipped cream into a piping bag and pipe the cream over the top of the bananas.
To serve, carefully remove the tart tin and transfer the pie to a serving plate. Drizzle over the melted white and dark chocolate and serve.
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