Preheat the oven to 350°F. Cream butter and sugar in a bowl until light and fluffy. Add eggs, sour cream, bananas, and vanilla; mix well. Combine flour, baking powder, and baking soda, and add to egg mixture; mix well. Stir in pecans. Pour into a greased 9x5-inch loaf pan. Bake for 55 minutes, or until loaf tests done.