Preheat oven to 350F. Grease and flour one 9x13 inch pan, or two 7x3 inch loaf pans. (or line with parchment paper)
Combine banana and sour cream. Set aside.
1 cup mashed bananas, 1 cup sour cream
In a large bowl, cream together the butter and sugar until smooth. Beat in the eggs one at a time, then stir in the vanilla and the banana mixture.
¼ cup butter, 1 ⅓ cups white sugar, 2 eggs, 1 teaspoon vanilla extract
Combine the flour, baking soda, baking powder and salt; stir into the banana mixture. Spread the batter evenly into the prepared pan or pans.
2 cups all-purpose flour, 1 teaspoon baking soda, 1 teaspoon baking powder, ¼ teaspoon salt
For a 9x13 pan: Bake 40-50 minutes, until a toothpick inserted in the center comes out clean. For loaf pans: Bake for 50-55 minutes in the preheated oven, or until a toothpick inserted into the center of the bread comes out clean.