In another bowl, cream the butter with the oil, sugar, and vanilla with an electric mixer. Add the eggs, one at a time and beat until incorporated. At low speed, add the dry ingredients alternately with the milk and bananas. Spread in the pan. Bake for about 1 hour and 15 minutes or until a toothpick inserted in the centre of the cake comes out clean. Let cool. Unmould and cool completely on a rack.
Mars Bar Ganache