Preheat oven to 350 degrees F (175 degrees C). Grease and flour one 9×13 inch pan, or two 7×3 inch loaf pans.
Combine banana and sour cream. Set aside. In a large bowl, cream together the margarine and sugar until smooth. Beat in the eggs one at a time, then stir in the vanilla and banana mixture. Combine the flour, baking soda, baking powder and salt; stir into the banana mixture. Spread the batter evenly into the prepared pan or pans.
Bake for 50 minutes in the preheated oven, or until a toothpick inserted into the center of the bread comes out clean.
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