Preheat oven to 350 degrees an line a muffin tin with paper or silicon cups.Peel bananas and mash them in a bowl. Set aside.In a large bowl, combine flour, baking powder, baking soda, salt and light brown sugar. Make a well in the center an add buttermilk, beaten egg, olive oil (or butter) and bananas.
Combine until just mixed. Do not overmix!
Add in blueberries and give a couple of stirs.Spoon batter into muffin cups until full and then sprinkle the tops with raw sugar.
Bake for 20 - 25 minutes until golden brown.
Let cool a few minutes in the pan and then transfer to a wire rack to cool completely.