Preheat oven to 350 degrees F.
Beat butter until lightened in color, add sugar, scraping down sides and continue to beat until light and fluffy. Add eggs and crushed bananas all at once and mix until combined.
In another bowl, mix together flour, baking soda, and salt. Add to banana mixture and mix until just combined. Add vanilla (or rum) and turn into a well-greased and floured 9 x 5″ pan.
Bake for about an hour to an hour and ten minutes, until a tester comes out with a few moist crumbs. Remove from oven and cool on a rack for 15 minutes or so, covered by a clean towel. Turn out bread.