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

In a medium bowl, using an electric mixer, beat the softened cream cheese, 1/4 cup granulated sugar, egg yolk, and 1/2 tsp vanilla extract until smooth and creamy. Set aside.

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

In another large bowl, whisk together the melted and cooled butter, 1/2 cup granulated sugar, and light brown sugar until well combined.

Whisk in the eggs one at a time, ensuring each is fully incorporated before adding the next. Stir in 1 tsp vanilla extract.

Fold in the mashed bananas and sour cream until just combined.

Gradually add the dry ingredient mixture to the wet ingredients, mixing with a rubber spatula until just combined. Be careful not to overmix; a few lumps are fine.

Pour about half of the banana bread batter into the prepared loaf pan. Spoon dollops of the cream cheese mixture over the batter.

Carefully spoon the remaining banana bread batter over the cream cheese dollops. Use a knife or skewer to gently swirl the cream cheese into the banana bread batter, making sure not to overmix or reach the very bottom of the pan with the swirl.

Bake for 60-70 minutes, or until a wooden skewer or toothpick inserted into the banana bread (avoiding the cream cheese swirl directly) comes out clean. If the top starts to brown too quickly, you can tent it loosely with aluminum foil.

Let the banana bread cool in the pan for 10-15 minutes before carefully inverting it onto a wire rack to cool completely. Slice and serve.