Preheat and Prep: Preheat oven to 350°F (175°C). Grease a 9×5-inch loaf pan with butter or cooking spray. Set aside.
Make the Banana Bread Batter: In a large bowl, mash bananas until smooth. Add melted butter, brown sugar, egg, and vanilla. Mix until well combined. Add flour, baking soda, and salt. Fold gently until flour just disappears. Do not overmix.
Make the Cinnamon Swirl: In a small bowl, stir together brown sugar, cinnamon, and 1 tsp of flour until evenly combined.
Layer and Swirl: Pour half the batter into the prepared loaf pan. Sprinkle all but 2 tablespoons of the cinnamon-sugar evenly over batter. Top with remaining batter. Sprinkle reserved cinnamon-sugar on top. Swirl with a butter knife: 3 passes lengthwise, 3 widthwise. Stop — do not over-swirl.
Bake: Bake 55–65 minutes until toothpick comes out clean or internal temp reads 200–205°F (93–96°C). Tent with foil after 40 min if browning too quickly. Cool in pan 10 min, then transfer to a rack. Cool completely (at least 30 minutes) before glazing.
Make the Cream Cheese Glaze: Beat cream cheese with a hand mixer until smooth. Add sifted powdered sugar and vanilla. Mix in milk 1 tablespoon at a time until drizzleable consistency. Drizzle over fully cooled loaf.
