Rub flour and butter together until the mixture resembles fine breadcrumbs.
Mix in cold water to form a soft dough.
Roll out dough on a floured surface and line a 20cm flan tin.
Chill the pastry in the fridge for 30 minutes.
Preheat the oven to 200°C.
Bake blind with foil and beans for 15 minutes.
Remove beans and foil and bake for 5 more minutes to dry the base.
Melt butter and sugar in a pan, then stir in condensed milk.
Stir for 5 minutes until thick and golden, then pour into the pastry case to cool.
Whip double cream until it holds its shape and spread over the cold toffee.
Top with sliced bananas dipped in lemon juice and sprinkle with grated chocolate.
Chill the pie before serving.