Preheat the oven to 350º.
Lightly butter one 8-by-4 inch loaf pan.
Mix the dry ingredients in a large bowl and add the toasted walnuts
In a medium bowl, whisk two eggs, oil, sour cream and vanilla.
Stir the banana into the egg mixture, then fold into the dry mixture until just combined.
Spread the batter in the prepared pan and bake for 50 minutes to 55 mins, or until a toothpick inserted in the center comes out clean. Cool completely before serving.