Preheat oven to 350°.
Line muffin tin with paper liners.
In a medium bowl, mix together flour, baking soda, baking powder, and salt.
In the bowl of an electric mixer, beat butter, sugars, and vanilla in a large bowl until light and fluffy.
Add eggs 1 at a time, beating just until blended.
Add bananas and beat just until blended.
Add in sour cream.
Add half of the dry ingredients, then the buttermilk, then the remaining dry ingredients.
Stir in chocolate.
Spoon into muffin tin and bake at 350° for 30 minutes or until a wooden pick inserted into the center comes out clean. Remove cupcakes to a wire rack and let cool completely.