Preheat your oven to 350°F (175°C).

Grease a 9x5x3-inch loaf pan generously with softened butter, then sprinkle some granulated sugar on top.

Whisk together the flour, baking soda, and salt in a bowl until well-combined.

Mix the milk, white vinegar, and vanilla extract in a separate bowl; let it sit for a few minutes.

Cream together the softened butter and granulated sugar in a mixing bowl until fluffy and light.

Mash the overripe bananas in another bowl. Add them to the butter-sugar mixture along with the eggs, mixing well.

Combine the dry ingredients and wet mixture, alternating with the milk mixture. Stir gently until just blended.

Fold in the blueberries gently.

Pour the batter into the prepared loaf pan, spreading it evenly.

Mix the cinnamon and sugar together, then sprinkle it over the batter.

Bake in the preheated oven for 45-50 minutes, or until a toothpick inserted in the center comes out clean.

Cool the bread in the pan for 15-20 minutes, then carefully transfer it to a wire rack to cool completely.