Preheat the oven to 350°F. Be sure to adjust the oven rack to the lower-middle position.
Grease a 9x5-inch light-colored loaf pan or line it with parchment paper. Set aside.
In a large mixing bowl, whisk together the mashed bananas, sugar, peanut butter, oil, buttermilk, eggs, and vanilla.
3 overripe bananas, ~1 1/4 cup mashed, 1 cup granulated sugar, 1/2 cup creamy peanut butter, 1/4 cup vegetable oil, 3 Tbsp. buttermilk, room temperature, 2 eggs, room temperature, 1 tsp. vanilla extract
In another bowl whisk together the dry ingredients.
2 cups all purpose flour, spooned and leveled, 2 Tbsp. cornstarch, 1 tsp. kosher salt, 3/4 tsp. baking soda
Add the dry ingredients into the banana mixture and fold in with a rubber spatula until mostly combined.
Add chocolate chips and fold until combined, being careful not to over-mix.
1/2 cup mini chocolate chips
Pour into the prepared pan, smoothing out the top. Bake ~60-65 minutes or until a toothpick inserted into the middle comes out clean. The batter will appear set, and the tops will be golden brown.
Let the bread cool in the pan on a wire rack for ~30 minutes. Remove it from the pan, cool completely, and then make the glaze.
In a microwave-safe bowl, melt the peanut butter, butter, and milk in 30-second intervals until melted. Whisk together, and then add powdered sugar and vanilla extract. Whisk until smooth, adjusting ingredients to reach the desired consistency: add a splash of milk for a thinner glaze or more powdered sugar if you prefer it thicker.
1/3 cup creamy peanut butter, 2 Tbsp. unsalted butter, 2 Tbsp. whole milk, or more as needed, 1 cup powdered sugar, 1/2 tsp. vanilla extract
Spread on top of cooled bread, slice, and enjoy.