Step 1

Preheat oven to 350F. Butter the bottom and sides of a 9×13 inch metal baking pan. Put a long piece of parchment paper in the bottom of the pan, letting the parchment extend up two sides of the pan and overhang slightly on both ends. Place another piece of parchment paper in the same manner, perpendicular to the first sheet. (This will make it easy to remove the bars from the pan after they have baked.) Butter the parchment.In a large bowl whisk together the flour, baking soda, and salt; set aside.

Step 2

In the bowl of a stand mixer fitted with the paddle attachment beat the butter and sugar on medium speed until light and fluffy, about 3 minutes. Beat in the eggs, one at a time, then stir in the sour cream, vanilla, and banana extract. Add flour mixture and mix until just combined. Fold in the mashed banana. Transfer the batter to the prepared pan, smoothing the top. Bake 22-25 minutes. or until toothpick inserted into the center comes out with just a few moist crumbs attached. Transfer pan to wire rack to cool completely.

Step 3

To make the cream cheese frosting: In the bowl of a stand mixer fitted with the paddle attachment combine the cream cheese and butter until smooth. Add the sugar and mix at low speed until combined. Stir in the vanilla and mix again. Spread on cooled banana bars.