Prepare the Oven and Pan: Preheat the oven to 350°F (175°C). Grease a 9 x 5-inch (23 x 13 cm) metal loaf pan. Line the bottom and long sides with parchment paper, leaving enough overhang to lift out the baked loaf. This preparation ensures easy removal of the bread after baking.

Make the Cinnamon Filling: In a small bowl, stir together the brown sugar, flour, and cinnamon. Add the melted butter and mix until the filling resembles damp, loose crumbs. Set it aside while preparing the batter. This filling will create the signature cinnamon swirl in the bread.

Mash the Bananas: Place the peeled bananas in a large mixing bowl. Mash them with a fork until mostly smooth. A few small pieces are fine, but large chunks can create wet pockets inside the loaf. Properly mashing the bananas ensures even distribution throughout the batter.

Combine the Wet Ingredients: Add the melted butter and brown sugar to the mashed bananas and whisk until evenly blended. Add the eggs, sour cream, and vanilla, then whisk until the mixture looks smooth and no streaks of egg or sour cream remain. This step is crucial for achieving a uniform batter.

Mix the Dry Ingredients: In a medium bowl, whisk together the flour, baking soda, baking powder, and salt. Break up any compacted flour so the leavening is distributed evenly. Properly mixing the dry ingredients helps ensure the bread rises well during baking.

Finish the Batter: Add the dry ingredients to the banana mixture. Fold gently with a flexible spatula until only a few small flour streaks remain. Stop mixing as soon as the batter is uniform. It should be thick and slowly spread from the spatula. Overmixing can lead to a tough texture.

Create the First Layer: Spread approximately one-third of the banana batter evenly in the prepared pan. Sprinkle one-third of the cinnamon filling over the batter, keeping a narrow border around the sides. This layering technique helps create distinct swirls in the finished loaf.

Repeat the Layers: Add half of the remaining batter and spread it gently without disturbing the cinnamon layer. Sprinkle with half of the remaining filling. Add the final portion of batter and finish with the remaining cinnamon mixture. Layering this way ensures an even distribution of flavors.

Swirl the Filling: Insert a butter knife or thin skewer into the batter and draw it through the loaf in two or three shallow figure-eight motions. Do not over-swirl, or the cinnamon filling may blend completely into the batter and create dense pockets. This step is key to achieving the desired swirl effect.

Bake the Loaf: Bake on the center rack for 55 to 65 minutes. The top should be deeply golden and lightly cracked, and a toothpick inserted into the center should come out clean or with a few moist crumbs. Avoid testing directly through a cinnamon ribbon, as this may give a false reading.

Protect the Top if Needed: If the loaf becomes dark before the center is done, loosely cover the pan with aluminum foil after about 40 minutes. Continue baking until no wet batter appears on the toothpick. This prevents the top from burning while ensuring the loaf is fully baked.

Cool in the Pan: Place the pan on a wire rack and let the bread cool for 20 minutes. The loaf will be delicate while hot, so lifting it immediately may cause it to split. Allowing it to cool slightly helps it set before removal.

Finish Cooling: Use the parchment overhang to lift the loaf from the pan. Place it directly on the wire rack and cool for at least 1 hour 10 minutes, or until completely cool. Proper cooling is essential for the glaze to adhere correctly.

Make the Cream Cheese Glaze: Beat the softened cream cheese in a small bowl until smooth. Add the powdered sugar, milk, and vanilla, then mix until the glaze is thick but pourable. Add additional milk 1 teaspoon (5 ml) at a time only if needed. The right consistency is important for even glazing.

Glaze the Loaf: Spoon or drizzle the glaze over the cooled banana bread. Let it stand for about 10 minutes, until the surface of the glaze begins to set. This resting time allows the glaze to firm up slightly.

Slice and Serve: Cut the loaf into 10 slices with a serrated knife. Wipe the blade between cuts if the cinnamon filling or glaze begins to stick. This ensures clean slices for presentation.