Preheat the oven to 350°F / 175°C. Butter a 1 lb. loaf pan and line it with parchment paper, to create a "hammock" for lifting the bread later on.
In a small bowl, mix together the blueberries and 1 tbsp. all purpose flour until all the blueberries are coated. Set aside.
In a small microwave safe bowl, melt the butter in 20 second intervals, stirring after each interval until it's just completely melted.
In a medium sized mixing bowl, mash up the banana until only a few small chunks remain.
To the banana, mix in the melted butter and brown sugar.
Add in both eggs, vanilla, and sour cream. Whisk vigorously until the mixture is well combined.
Add in the flour, baking powder, baking soda, salt, and cinnamon. Gently mix the ingredients together until only a few streaks of flour remain. Then, add in the blueberries and mix just until no flour streaks remain.
Pour the batter into your prepared loaf pan. Top the batter with the crushed pistachios, very gently pressing the pistachios down so they stick to the batter.
Bake for 55-65 minutes.* For the best doneness test, I recommend using a thermometer. Insert a thermometer into the center of the cake about half way down. When it reads 205°F / 96°C, it's ready to be taken out.
Allow the cake to come to room temperature before slicing. Once it's room temperature, slice, serve, and enjoy!