For the caramel, 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, to make the caramel. As soon as the mixture thickens and begins to smell of caramel, remove from the heat and allow to cool.
Meanwhile, for the banoffee pie, place the crushed biscuits and 115g/4oz of the pecans into a bowl. Add the butter and mix well.
Transfer the mixture to a 25cm/10in cake tin. Press in to pack the mixture evenly into the base.
Add the chopped bananas to the caramel mixture and mix well, then spread the mixture over the biscuit base.
Transfer to the refrigerator to cool for 30 minutes.
Remove from the fridge and spread the whipped cream evenly over the top of the banoffee layer.
Place the remaining pecans over the top in a circular arrangement and dust with cocoa powder.
For the caramel sauce, place the butter, sugar and coconut milk into a heavy-based pan over a medium heat. Bring to the boil and cook for 3-4 minutes, until it forms a thick, light golden-brown sauce.
To serve, cut out slices of the banoffee pie, place onto plates and pour over the caramel sauce.