To make the caramel, place the butter and the sugar in a non-stick pan over a low heat. Stir until the butter melts and the sugar has completely dissolved.
Add the condensed milk to the same pan and slowly bring to the boil, stirring continuously. As soon as the mixture thickens and starts to smell like caramel, remove the pan from the heat and allow to cool.
For the banoffee pie, place the crushed McVitie’s digestives in a bowl with the pecans and the butter and mix well.
Transfer this base mixture into a 25cm cake tin and press down to ensure that the mixture is level.
Add the sliced bananas to the caramel mixture and stir. Spread evenly over the biscuit base. Transfer to the fridge and allow to cool for 30 minutes.
Whip the cream into soft peaks and spread it over the banoffee layer.
Melt the dark chocolate in a glass bowl over a pan of simmering water and drizzle it over the top of the pie.