Line a 23cm spring release pie tin with baking paper.
Toffee Remove the label from the condensed milk tin. Place the unopened tin in a deep saucepan and fill with water about 3cm from the top of the saucepan, ensuring that the tin is completely immersed in water. Bring the water to the boil and boil steadily for 3 to 4 hours. Keep the kettle handy and add boiling water to the saucepan regularly; check every 20 to 30 minutes. Ensure that the saucepan never boils dry and that the tin is always completely immersed in water, otherwise the tin will explode! After boiling, remove tin from water with a pair of tongs and allow to cool 10 to 15 minutes before opening. Do not open the tin until it is cool enough to handle.
Base: Crush the biscuits to make breadcrumbs. In a bowl combine with the melted butter. Press the mixture into the prepared pie tin, pressing halfway up the sides. Chill the base for at least 1 hour.
Filling: Whip the cream using a stand or hand-held electric mixer. Beat on high speed for 3 to 5 minutes, or until stiff peaks form.
Slice the bananas into half centimeter rounds.
To Assemble: Arrange a layer of sliced bananas over the biscuit base using 1/2 of the bananas. Drizzle about 1/4 of the cooled toffee over the banana layer. Repeat with the remaining bananas and toffee.
Generously spread the whipped cream over the toffee layer, ensuring it is spread evenly to the edge of the tin.
Grate the chocolate over the top of the pie. Refrigerate until ready to serve but about 1 to 3 hours.