Preheat oven to 350 degrees. Grease and flour a 13x9-inch baking pan.
With an electric mixer, cream together the butter and sugar. Add eggs, one at a time, and mix well after each addition.
Stir in mashed bananas, buttermilk, and vanilla.
In a medium bowl, mix flour and baking soda. Add to banana mixture, stirring well to combine.
Pour into baking pan and bake for 35 minutes. Cool completely before frosting.
For frosting, melt butter in saucepan over medium-low heat. Add brown sugar and cream. Cook for about 2 minutes, until sugar has dissolved, stirring frequently.
Remove from heat and add vanilla. Using a handheld mixer, beat in confectioners' sugar, about ½ cup at a time, until smooth. Spread evenly onto cake and allow to set before cutting.
Recipe by Simple, Sweet & Savory at https://www.simplesweetsavory.com/banana-cake-caramel-frosting/