Preheat your oven to 350°F (175°C) and prepare a 9 x 5 loaf pan.

In a large bowl, whisk together the all-purpose flour and baking soda. Set aside.

In another bowl, mix melted butter, granulated sugar, sour cream, eggs, mashed bananas, and vanilla extract until combined.

Pour the banana mixture into the dry ingredients and mix gently until just combined.

Transfer the batter into the prepared loaf pan, spreading evenly and tapping to remove air bubbles.

Mix brown sugar and cinnamon, and sprinkle it over the batter, swirling gently with a knife.

Bake for 65 to 70 minutes, checking for doneness with a toothpick.

Remove from oven and let cool in the pan for 10-15 minutes before transferring to a wire rack.

Whisk together powdered sugar, milk, and vanilla for the drizzle topping.

Once cooled, drizzle the topping over the loaf and slice before serving.