Mix flour, sugar, baking powder, baking soda, and salt in a bowl.
Stir in bran.
Add butter and cut in with pastry blender or 2 knives until pieces are fine.
Combine sour cream, banana, and milk.
Add to dry ingredients and mix lightly with a fork until flour is moistened.
Turn dough onto an ungreased baking sheet.
Pat into a square about 3/4 inch thick.
Mark with a knife into 12 squares.
Bake at 450°F about 15 minutes.