Preheat the oven to 350°F. Line a 9-inch loaf pan with parchment paper then grease the parchment paper with cooking spray.
In a large bowl, whisk together 2 cups of flour with the sugar, baking soda, cinnamon and salt. Set the bowl aside.
In a separate medium bowl, whisk together the mashed bananas, buttermilk, eggs, melted butter and vanilla extract.
Add the wet ingredients to the dry ingredients and stir just until combined.
In a small bowl, combine the diced apples with 1 Tablespoon flour, tossing until they’re thoroughly coated. Fold in the diced apples then pour the batter into the prepared loaf pan. Sprinkle the top liberally with sanding sugar (optional).
Bake the bread for about 55 minutes, or until a toothpick inserted comes out clean. Remove the bread from the oven and allow it to cool in the pan for 10 minutes before transferring the loaf to a cooling rack to cool completely.