- Sieve the flour, icing sugar and cornflour into a bowl. Rub in the margarine until mixture resembles fine breadcrumbs. Press into a greased and lined loose bottomed 23cm / 9" cake tin. Bake in a preheated oven 350°F/180°C/Gas 4 for 20 minutes approx. until golden in colour. Allow to get cold in the tin.
- Place the tin (unopened) of condensed milk in a saucepan covered with sufficient water to cover top of tin. Bring to the boil and then reduce to a low simmer for 3 hours. Remove tin from saucepan and allow to cool. This can be done a few days in advance.
- Spread toffee over the cold shortbread. Gently remove from the cake tin and place on a serving plate. Arrange the sliced bananas on the toffee, cover with the whipped cream and top with grated or flaked chocolate.
Make sure the level of the water does not fall below the tin of condensed milk during simmering.