Preheat oven to 400 degrees. Grease or line a 12-cup muffin tin.
In a small bowl, mash the bananas and set aside. In a large bowl, whisk together flour, baking powder, baking soda, cinnamon and salt. Add in brown sugar, white sugar, melted butter, eggs, vanilla and sour cream. Blend and mix in mashed bananas.
To make the streusel, using a small bowl, combine the flour, cinnamon and salt. Using two forks or your fingers, cut butter into the flour and sugar mixture until it resembles coarse crumbs.
Divide batter evenly between greased or lined muffin cups and top with streusel. Bake at 400 degrees for five minutes. Lower oven to 375 degrees and bake for an additional 13-15 minutes.