In a medium sized bowl, combine the flour, sugar, baking powder, baking soda and salt. Stir with a whisk to combine. Add oats and stir to combine.
1 ½ cups flour, ⅔ cups sugar, 1 ½ teaspoons baking powder, ¼ teaspoon baking soda, ¼ teaspoon salt, ¾ cups old fashioned rolled oats
In a separate medium sized bowl, combine the banana, eggs, buttermilk, vegetable oil, and vanilla. Stir to combine.
1 cup mashed ripe banana (about 2-3 large), 2 eggs, lightly beaten, ⅓ cup buttermilk, ¼ cup vegetable oil, 1 teaspoon vanilla
Add the banana mixture to the flour mixture and stir just until combined and you no longer see any of the dry ingredients.
1 cup blueberries
Carefully fold in the blueberries just until incorporated.
Tightly cover and place muffin batter in the refrigerator for at least an hour.
Spray the top of a muffin tin with cooking spray. Line cups with muffin liners.
Preheat oven to 425°. Fill muffin liners ¾ of the way full.
Bake at 425° for 9 minutes. Reduce temperature to 350° and continue to bake for 7-9 additional minutes or until the muffins are lightly browned and a toothpick inserted into the middle comes out clean. Do not over bake or they will be dry.
Let them cool in the muffin tin for 5 minutes and then carefully remove and transfer to a cooling rack to cool completely.
Place the turbinado sugar in a small bowl. Brush the tops of the muffins with the melted butter and roll the tops in the sugar, carefully coating the entire muffin top.
2 tablespoons butter, melted, ½ cup turbinado sugar