Preheat oven to 350 degrees F (175 degrees C). Grease and flour one 9x5 inch pan.
Cream butter and sugar until smooth. Beat in eggs, vanilla and then bananas. Add flour and soda, stirring just until combined.
Pour into prepared pan and bake at 350 degrees F (175 degrees C) for about 1 hour (or till toothpick comes out clean). If you need to cook longer than an hour place tin foil over bread and bake in 5 minute increments. Remove from pan and let cool, store in refrigerator or freeze.