Preheat the oven to 350°F (175°C). Grease a 10x15-inch jelly roll pan that's at least 1 inch deep and set it aside.

In a large mixing bowl, cream the softened butter, granulated sugar, and brown sugar until light and fluffy, about 5 minutes.

Add the eggs, one at a time, beating well after each addition. Beat in the mashed bananas, sour cream, and vanilla extract until well combined.

In a separate bowl, whisk together the all-purpose flour and baking soda.

Gradually add the dry ingredients to the banana mixture, mixing until combined. Do not overmix.

Spread the batter evenly into the prepared baking pan. You may tap the pan on the counter a few times to even out the filling.

Bake in the preheated oven for 20-25 minutes or until a toothpick inserted into the center comes out clean and the top is golden brown.

Remove from the oven and let cool completely in the pan on a wire rack.

In a medium mixing bowl, beat the softened butter and cream cheese until smooth and creamy.

Add the vanilla extract and pinch of salt, and beat until well combined.

Gradually add the confectioner's sugar, beating well after each addition until the frosting is smooth and spreadable. Adjust the amount of confectioner's sugar to achieve desired sweetness and consistency.

Once the banana bars are completely cooled, spread the cream cheese frosting evenly over the top. For easier spreading, slightly warm the frosting in the microwave for a few seconds.

Optional: Garnish with sliced bananas or chopped nuts if desired.

Cut the frosted banana bars into squares or rectangles. Serve and enjoy these delicious banana bars with cream cheese frosting! Any leftover banana bars can be stored in an airtight container in the refrigerator for up to 3-4 days.