
Preheat oven to 350℉ (180℃). Grease a 9×5 loaf pan with cooking spray or butter.
In a small bowl, mix the mashed bananas, pumpkin puree, sour cream, and eggs.
Add the brown sugar, granulated sugar, and vanilla to the batter, and mix until smooth.
Gradually mix the dry ingredients into the wet ingredients: flour, baking powder, baking soda, cinnamon, nutmeg, ginger, allspice, orange zest, and salt until fully combined.
Pour in the melted butter and continue stirring until the butter has been fully incorporated into the mixture.
Scrape down the sides, add chocolate chips if using, then pour the batter into the greased pan and spread evenly. Or divide the batter between two smaller greased bread pans.
Add the desired toppings or leave the bread plain.
Bake for 55-60 minutes. If you divided the batter between two bread pans, start checking it at 30 minutes. Bake until a cake tester inserted into the center comes out clean.
Let the pumpkin banana bread remain in the pan(s) for about 10 minutes before removing, then turn it out onto a wire rack to cool completely.
While the bread is cooling, make the optional glaze. Mix the powdered sugar, melted brown butter, vanilla, and milk until well combined. Adjust to the desired consistency with milk or powdered sugar, and drizzle it on the cooled bread.