• Preheat oven to 350 deg F and line a 15x10x1 baking pan with parchment paper. Set it aside.
• In a large mixing bowl, using a stand/handheld mixer, beat butter and granulated sugar till the butter gets super fluffy and turns light in color. About 2-3 minutes. Next add in eggs, one at a time and beat well after each addition.
• Add in sour cream and vanilla. Mix them well to combine. Now add flour, baking soda and salt to the butter mixture and beat on low speed just till flour disappears into the batter. Add and mix in mashed bananas too.
• Transfer the batter into pre-lined pan and bake for 20-25 minutes or till a toothpick inserted in the center comes out clean. Set the pan over a wire rack and allow the bars to cool down completely in the pan. Let the bars cool completely before frosting.

For the Caramel Frosting:

• In a large sauce pan, add sugar and moisten it with water. Bring it to a boil, stirring constantly. Once it comes to a boil, stop stirring and allow the sugar to caramelize. Swirl the pan occasionally and cook till sugar gets a dark amber color.
• Now remove form heat and pour in the milk. It bubbles a lot at this stage so be careful. Stir until the mixture gets smooth. Next add in half a stick of butter (from the cubed butter) and vanilla to the caramelized sugar mixture. Mix till butter melts. Allow the mixture to cool down to room temp in refrigerator.
• Now beat the butter using a hand beater or stand mixer till it turns light. Slowly add in all the confectioners' sugar and continue beating. Scrape the bowl as desired. Gradually add the remaining 1 stick of cubed butter in and allow it to mix well before adding more.

  Once all the butter is in, beat for an extra minute and frost as desired.