Step 1: Crush digestive biscuits into fine crumbs and mix with melted butter until well combined.
Step 2: Press the biscuit mixture firmly into a 9-inch pie dish to form an even base, then chill for 30 minutes.
Step 3: Place unopened can of condensed milk in a saucepan, cover with water, and boil for 2 hours to make caramel (toffee).
Step 4: Carefully open the cooled can and spread the thick caramel evenly over the chilled biscuit base.
Step 5: Arrange sliced bananas in a single layer over the caramel.
Step 6: Whip heavy cream with powdered sugar and vanilla until stiff peaks form, then spread over bananas.
Step 7: Garnish with dark chocolate shavings and chill for at least 2 hours before serving.