Preheat oven to 350°F (175°C). Grease and flour a 9x5 inch loaf pan, or line with parchment paper leaving an overhang on the long sides for easy lifting.

In a large mixing bowl, whisk together the all-purpose flour, granulated sugar, baking soda, salt, and ground cinnamon until well combined. Set aside.

In a medium mixing bowl, mash the very ripe bananas with a fork or potato masher until mostly smooth with a few small lumps remaining. Add the melted and cooled unsalted butter, eggs, vanilla extract, and milk to the mashed bananas. Whisk until thoroughly combined.

Pour the wet banana mixture into the dry ingredients. Using a rubber spatula, gently fold until just combined. Be careful not to overmix; a few lumps of flour are okay. Overmixing will result in tough bread.

Gently fold in the blueberries (which have been tossed in 1 tbsp flour) until evenly distributed throughout the batter. Tossing them in flour helps prevent them from sinking to the bottom of the loaf.

Pour the batter into the prepared loaf pan and spread evenly. If desired, sprinkle the top with turbinado sugar for a lovely crunchy crust.

Bake for 50-60 minutes, or until a wooden skewer or toothpick inserted into the center comes out clean or with moist crumbs, but no wet batter. If the top starts to brown too quickly, you can tent it loosely with aluminum foil for the last 15-20 minutes of baking.

Let the banana bread cool in the pan on a wire rack for 10-15 minutes before carefully lifting it out (if using parchment paper) or inverting it onto the rack. Allow it to cool completely before slicing for the best texture, though it's also delicious warm!