Crush digestive biscuits into fine crumbs using a food processor or place them in a sealed bag and bash with a rolling pin. Mix with melted butter until the mixture resembles wet sand. Press firmly into a 23cm tart tin, creating an even layer across the bottom and up the sides. Refrigerate for 30 minutes to set completely.

In a heavy-bottomed saucepan, combine condensed milk, butter, and brown sugar over medium-low heat. Stir continuously for 8-10 minutes until the mixture thickens and turns a beautiful golden caramel color. You'll know it's ready when you can draw a line through it with your spoon and it holds for a few seconds.

Pour the warm toffee over the chilled biscuit base, spreading evenly with a spatula. Allow to cool completely, then refrigerate for at least 2 hours. Just before serving, slice bananas into rounds and arrange them over the toffee layer in overlapping circles.

Whip double cream with icing sugar until soft peaks form. Spread or pipe generously over the bananas. Sprinkle with dark chocolate shavings for an elegant finishing touch.