Preheat oven to 350 degrees Fahrenheit (175 degrees Celsius) and grease a 9x13 inch baking pan.

In a large bowl, combine the yellow cake mix, melted butter, and one egg until a thick dough forms.

Press the dough evenly into the bottom of the prepared baking pan to form the base layer.

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

Add the remaining two eggs, mashed bananas, and vanilla extract to the cream cheese and mix until fully incorporated.

Slowly beat in the powdered sugar until the topping mixture is smooth and free of lumps.

Pour the banana cream mixture over the cake base in the pan, spreading it to the edges.

Bake for 40 to 45 minutes until the edges are golden brown; the center should remain slightly soft and jiggly.

Remove from the oven and allow to cool completely on a wire rack for at least 2 hours before cutting into bars.