Preheat oven to 350 F. Grease and flour 9x5 inch loaf pan. Whisk together in a medium bowl the flour, salt, and baking soda. Set aside.
In a large mixing bowl, use an electric mixer to beat together the butter and sugar until fluffy.This should take about three minutes or so.
Add the eggs one at a time, beating well after each addition. Scrape the bottom and sides of the bowl as needed.
Add the bananas, sour cream, and the vanilla and beat until incorporated. Beat it flour and the chocolate just until incorporated. Do not overbeat.
Pour batter into the loaf pan and bake for 50-60 minutes. A toothpick inserted at the center of the bread should come out clean. Some bits of melted chocolate may be present. Let cake cool slightly in the pan and then transfer to a wire rack to cool completely.
Recipe adapted from Martha Stewart