Preheated the oven to 180° C/Gas Mark 4.
Cream the butter and sugar together until light and fluffy. Mix in the eggs and add in the sieved flour and melted chocolate, mix well.
Divide the mixture into two 20cm, greased and lined cake tins.
Bake in the oven for 25-30 minutes, until a skewer inserted into the centre comes out clean. Leave to cool.
To make the toffee sauce; put butter, condensed milk, sugar and white in a pan. Cook gently till all the sugar is dissolved and keep stirring until the sauce thickens.
To serve, sandwich the banana slices in between the chocolate cake. Cut a slice of the cake and place it on a warm plate. Arrange the banana around the cake and serve with whipped cream.