Preheat oven to 350. Line a 9x5" loaf pan with parchment or spray with nonstick cooking spray and set aside.

Slice the bananas. Set aside.

Over medium heat, melt 4 tablespoons butter. Add the sliced bananas and brown sugar and sauté for about 4 minutes, stirring frequently. The sugar should turn into a light caramel and come to a mild simmer.  It's okay for the bananas to get broken up a bit as you stir. Remove from heat and cool for 10 minutes.

Place the banana mixture in a large bowl or the bowl of an electric stand mixer. Beat on medium speed until mostly smooth- it's normal to still have some banana pieces. 

In a large measuring glass, combine the buttermilk, oil, vanilla and eggs and whisk to combine. In a separate bowl, whisk together the flour, baking soda, and salt. Beginning and ending with the flour mixture, alternately add it to the banana mixture, mixing on low speed until just combined.

Pour the batter into the prepared baking pan. Bake for 45-60 minutes or until golden brown on top and a pick inserted into the center comes out with moist crumbs clinging to it. Cool for 10 minutes and then remove the bread from the pan and cool completely on a wire rack.

To prepare the glaze, melt 2 tablespoons of butter in a small saucepan or skillet over medium-high heat for 2-3 minutes or until it begins to get brown specks in it and smells nutty and fragrant. Whisk in the powdered sugar and use a tiny bit of milk if needed to get smooth consistency.  Drizzle over the bread when it's just barely warm. Slice and serve.