In a large mixing bowl, using either a stand mixer or an electric hand mixer, cream the butter with the brown sugar and sugar. Add the eggs, one at a time, incorporating well. Scrape the bottom and sides of the bowl with a rubber spatula occasionally. Add the bananas, vanilla extract and sour cream to the mixture and combine. Add the flour, baking soda, baking powder, and salt, stirring to combine. Once mixed thoroughly, fold in the pecans.