Preheat oven to 400 degrees. Lightly grease 12 2-1/2 inch muffin cups.
Combine flour, baking powder, salt, and cinnamon in a bowl. Beat bananas in a large bowl with an electric mixer until mashed. Add eggs, brown sugar, butter, and vanilla, beating until blended. Stir in combined dry ingredients with a wooden spoon until just blended. Stir in blueberries until just combined. Spoon into prepared muffin cups, dividing batter equally. Sprinkle tops of muffins with granulated sugar and