Preheat oven at 350°F.
Prepare 2 medium bread pans (8.5 x 4.5) or 1 large bread pan. Spray the pans and put parchment at the bottom of the bread pan(s). Spray the parchment paper as well.
Take 2 bananas and whip them in blender to make 1 cup of mashed bananas. Set aside.
Chop the pecans to make a ½ cup. Set aside.
In a separate bowl, sift flour, baking soda, baking powder, and salt. (If you don't have a sifter, you can whisk everything together in a bowl.) Set aside.
In a mixing bowl, beat the butter on high speed until fluffy. (About 1-2 minutes.) You can use a hand held electric mixer if you don't have a KitchenAid.
Gradually add the sugar. Continue beating until light and fluffy.
Beat in eggs 1 at a time. Add vanilla.
Turn the mixer on low. Alternately add the flour mixture and the sour cream to the sugar mixture. (Start and end with the flour mixture. Alternate between 3 additions of the flour mixture and 2 additions of the sour cream.) Mix until incorporated.
Add the mashed bananas and chopped pecans to the mixture. Mix just until it's blended.
Pour the batter into the prepared pan(s).
Bake for 40-60 minutes. If you are using a non-stick dark colored pan, it usually cooks in 40 minutes or so. If using a light colored pan, it takes about 53-60 minutes. Regardless of what pan you use, it's good to check it at the 40 minute mark to see if it's done. Bake until a toothpick comes out clean.
Cool the banana bread in the bread pan for 10 minutes. Then turn it onto a wire rack to cool completely.