Preheat oven to 180C Fan (160C if not using a fan oven)
Add flour, baking powder and bicrabonate or soda into a medium-large mixing bowl and hand whisk to combine.
Add banana, sugar, eggs, softened butter and vanilla to the blender container. Whizz together for 30 seconds - 1 minute until you have a smoothie like mixture with no lumps.
Pour the blended mixture into the flour mixture and whisk with the hand whisk or a spatula until just combined.
Add in frozen blueberries. I like to save a couple of blueberries to push into the top of the muffins once they are in the tray so you could do that - its a trick to make prettier muffins! The mixture will cool down when you do this so be ready to work quickly to get them in the muffin cases.
Fill cases to 3/4 full and pop in the oven for 6 minutes at the higher temerature.
After 6 minutes of baking reduce the oven temperature by 20 degrees C. and continue to cook for 15-18 more minutes until a toothpick inserted into the centre of the middle muffin in your tray comes back out with no wet mixture on it. A few crumbs is ok.
Leave the muffins to cool in the tray for 10 minutes before moving them to a cooling rack to cool fully
