Line the base and sides of a loaf pan with grease proof paper. Preheat oven to 150°C.
In a small bowl, combine the evaporated milk and vanilla essence, and mix well. Stir in the rum (if using). Cream the butter and brown sugar until light and fluffy. Add the eggs, one at a time, beating well.
Alternately, stir in the milk mixture and the dry ingredients (sifted twice together), a third at a time. Add the raisins and mix to distribute well.
Pour half the batter into the prepared loaf pan. Scatter some banana slices over. Top with the remaining batter and level the surface. Arrange the remaining banana slices on top.
Bake in the oven for 1 hour and 45 minutes. Halfway through baking, cover the top of the cake with a piece of aluminium foil. After 15 minutes, remove the foil and continue to bake until the cake is done – an inserted skewer should come out clean.