Preheat oven to 350 F / 175 C and grease an 8.5 in x 4.5 in loaf pan with non-stick spray or butter, I used the wrapper from the butter. Mash your over-ripe bananas and set aside. Add 1/4 cup unsalted butter and 1/2 cup granulated sugar into a large bowl. Beat on a medium high speed for 2-3 minutes with either a hand mixer or a stand mixer with a whisk attachment. Beat until the mixture becomes lighter in color and looks fluffier.

Mix in 1/4 cup vegetable oil and 1 large, whole egg + 1 egg white on a medium speed. Scrape the sides and bottom of the bowl as needed with a rubber spatula. Add in 1 cup of all-purpose flour, 1 1/2 tsp baking powder, 1/2 tsp baking soda, and 1/2 tsp salt. Mix on a low speed until just combined. Pour in 1/2 cup of buttermilk and mix on a low speed until incorporated. Add in the remaining 3/4 cup of flour and mix on low just until you can no longer see streaks of flour.

Mix in the mashed banana on a low speed until it is fully incorporated into the batter. Fold in 1 cup of roughly chopped Oreos. Pour the batter into the prepared pan.

Bake on the upper baking rack for 55-60 minutes, rotating the pan half way through to make sure it bakes evenly. If you notice the top of the loaf is browning quickly when you rotate it, cover the loaf pan with a foil tent to prevent it from over browning. (I did it on second rack from top and it didn’t burn). Remove the loaf from the oven and let it cool in the pan for 10 minutes. Transfer to a wire rack to finish cooling.

Place 1 cup powdered sugar, 2 Tablespoons milk, and 1 tsp of vanilla extract in a medium-sized bowl. Whisk together until smooth and no clumps remain. This glaze hardens as it sits, so cover it with plastic wrap if you don't plan to use it immediately. Pour on the cooled loaf of oreo banana bread and top with an additional 1/2 cup of chopped Oreos if desired.