Smash the biscuits up in a bag or food processor until you have an even crumb, then tip into a bowl.
Add the melted butter and the sugar to the biscuit crumb. Mix well to combine.
Grease a loose-bottomed 20cm (8 inch) sandwich tin and then tip the biscuit mix into it. Press the biscuit mix into the bottom and up the sides to create a case. It’s important the biscuit is packed down really tightly. Place in the freezer while you prepare the caramel.
To make the caramel, put the condensed milk, butter and sugar in a non-stick pan over a low heat.
Stir often as it gently bubbles. Be careful, it will be very hot. Don't leave it unstirred as it will easily burn. It will take about 10 minutes for it to thicken enough to hold its shape briefly when stirred. Generally speaking, for a sauce like this, you don't want the temp to exceed 180C (360F). If you're not sure if your caramel is too thick or thing, see the FAQ for extra tips.
Take the caramel off the heat and allow to cool to room temp or until still pourable but not piping hot as this will melt the biscuit base.
Retrieve the base from the freezer and make sure it feels really solid all over. If it doesn't, return to the freezer for another 10 minutes. Pour in the cooled caramel and allow it to settle and level off. It will be very thick now, so work gently.
When your caramel is completely cold, arrange the banana slices in a single layer.
Whip the cream into soft peaks and layer up on top of the banana generously – you might not need it all.
Grate the chocolate on top.
Return the banoffee pie to the fridge until you’re ready to serve.
To serve, carefully release the pie from the tin by standing it on a large can so that the sides drop away.
Now you can gently slide the case onto a plate – you can use a spatula to help – and serve in slices. Enjoy!
Keep it chilled – it won’t last long!
Store your banoffee pie uncovered in the refrigerator. Don't leave your pie sitting out on the counter. The bananas may soften and the fresh cream could spoil.