preheat oven to 350.
grease 9 inch loaf pan on all sides, dust with flour on all sides. shake off excess flour.
combine sour cream & baking soda in large bowl; let stand for 5 minutes.
Mix butter, sugar, eggs together in separate bowl, stir into sour cream mixture.
Add mashed banana, mix well.
gradually add vanilla & flour, mix well. Stir in chopped nuts.
pour batter into loaf pan, sprinkle additional chopped nuts & cinnamon sugar on top. bake 1 hour. To test when done, insert toothpick in center, if comes out clean then done. cool in pan 10 minutes, then turn onto wire rack.
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