In a large bowl, whisk together the flour, baking soda, baking powder and salt.
In a separate small bowl, mash the bananas with a wooden spoon, leaving a bit of texture.
In another large bowl, use a hand electric mixer or stand mixer to cream the 1/2 cup of butter and sugar together until light and fluffy.
Add the eggs, 1 at a time. Stir in the mashed bananas, sour cream and vanilla and beat until just combined.
Add the dry ingredients and gently stir in pecans.
Fill the prepared muffin cups halfway with batter.
Evenly distribute the pecan-crumb topping over the muffin batter.
Bake muffins for 18 to 22 minutes, or until a toothpick inserted into the center comes out clean.
Remove muffins from pan and let cool on wire rack for a few minutes.