Make the Crust:
Combine the crushed biscuits and melted butter in a bowl. Press the mixture evenly into the base and sides of a 9-inch pie dish. Chill in the refrigerator for at least 15 minutes to set.
Prepare the Toffee Filling:
In a saucepan, melt the butter and sugar over medium heat, stirring until dissolved. Add the sweetened condensed milk and bring to a gentle boil, stirring constantly. Cook for about 5 minutes until thickened and golden. Pour the toffee over the chilled crust and spread evenly. Chill for 1-2 hours until firm.
Assemble the Pie:
Once the toffee is set, layer the banana slices over the toffee filling.
Whip the Cream:
In a mixing bowl, whisk the heavy cream, powdered sugar, and vanilla extract until soft peaks form. Spread the whipped cream over the banana layer.
Garnish and Serve:
Sprinkle grated chocolate or sift cocoa powder over the whipped cream for a decorative finish. Slice and serve chilled.