In a large saucepan, melt butter over medium heat until it becomes nutty in flavor, brown in color and slightly foams. Remove from heat and allow to cool.
Meanwhile, in a small bowl, combine mashed banana and lemon juice. Set aside.
In a medium mixing bowl, combine flour, baking soda and salt. Set aside.
In a large in a mixing bowl or stand mixer, combine butter, sugar, and vanilla. Beat in eggs one at a time, until just combined.
Alternate adding flour mixture and buttermilk. Stir in banana mixture.
Pour batter into greased cake pan (reserving excess for an additional smaller cake or discarding).
Bake 1 hour 20 minutes or until a toothpick inserted into the center comes out clean. Remove from oven and place cake in freezer for 45 minutes.
Frosting
Meanwhile, in a stand mixer or medium mixing bowl, whip softened butter until smooth.
Gradually add powdered sugar. Blend in salted caramel sauce.
Remove cake from freezer and flip cake pan onto a cake platter. Frost cake. Top with bananas and cookies.