Preheat oven to 325 degrees F. Grease a a 9x5 inch loaf pan, line with a strip of parchment, grease again and dust with flour.
In a small mixing bowl, beat the softened cream cheese and sugar until smooth. Stir in the egg and vanilla. Set aside.
In a large bowl, whisk together flour, baking soda, salt and sugar. For best results, whisk for at least a minute to ensure all of the ingredients are thoroughly blended.
In a mixing bowl, mash the bananas, then add the eggs, oil, buttermilk and vanilla and stir until blended.
Add flour mixture to banana mixture and stir until combined.
Pour all but about 2 tablespoons of batter in the loaf pan. Spoon cream cheese mixture on top of batter, then spoon remaining 2 tablespoons of banana bread batter over so it has a marbled look.
Bake in the lower third of the oven for 60-70 minutes or until a toothpick inserted near the center comes out clean.
Let cool for 15 minutes. Loosen sides of loaves with a knife, then carefully turn from pan and let cool completely before slicing. If you want, chill slightly before serving so that the cream cheese mixture will be cool rather than room temperature.