Preheat oven to 350°F Sift together first four ingredients. Beat sugar and eggs with a whisk until light and fluffy. Drizzle in oil. Add bananas, sour cream, and vanilla. Fold in flour mixture and nuts. Pour batter into a buttered 9" x 4" loaf pan and bake for 45 minutes, or until a toothpick inserted in the center comes out clean.