Preheat the oven to 200C/180C Fan/Gas 6.
For the banoffee pie, put the flour in a bowl and rub in the unsalted butter with your fingertips until the mixture resembles fine breadcrumbs. Add the cold water gradually, mixing to form a soft dough. Roll out the dough on a lightly floured work surface and use it to line a 20cm/8in fluted flan tin. Put in the fridge to chill for 30 minutes.
Line the pastry case with baking paper and fill with baking beans or rice. Blind bake for 15 minutes, then remove the beans and baking paper and cook for a further 5 minutes to dry out the base. Remove from the oven and leave to cool.
Meanwhile, put the butter and sugar in a large saucepan and melt over a medium heat. Once melted add the condensed milk and mix. Pour into the cooled pastry case. Leave to set and cool.
Lay the sliced bananas on top of the caramel sauce, top with the whipped cream and garnish with the grated chocolate.
To make the marshmallows, lightly oil a shallow baking tray, about 30x20cm/12x8in and dust it with icing sugar and cornflour.
Soak the gelatine sheets in 140ml/4½fl oz cold water.
Put the sugar, glucose and 200ml/7fl oz water into a heavy-based pan. Bring to the boil and continue cooking for about 12-15 minutes until the mixture reaches 127C on a sugar thermometer. When the syrup is up to temperature, carefully slide in the softened gelatine sheets and their soaking water. The syrup will bubble up so take care not to burn yourself. Pour the syrup into a metal jug.
Whisk the egg whites until stiff, preferably with an electric whisk in a mixing bowl. Continue whisking while pouring in the hot syrup from the jug. The mixture will become shiny and start to thicken. Add the vanilla extract and continue whisking for about 5-10 minutes, until the mixture is stiff and thick enough to hold its shape on the whisk.
Spoon the mixture into the prepared tin and smooth with a wet palette knife if necessary. Leave for at least 1 hour to set.
Dust a work surface with icing sugar and cornflour. Loosen the marshmallow around the sides of the tray with a palette knife, and turn it out on to the dusted surface. Cut into squares and roll in the icing sugar and cornflour. Leave to dry a little on a wire rack.
For the caramelised bananas, heat a large frying pan and add the sugar, leave on the heat until it turns to caramel (CAUTION: boiling sugar is extremely hot. Handle very carefully.) Once turned to a caramel carefully add 4 tablespoons water to create a little sauce. Add the chopped baby bananas to the sauce and stir to coat.
To serve, put a slice of the banoffee pie in the centre. Garnish with a scoop of ice cream, squares of marshmallows, some caramelised bananas and sprinkle over the mint.