Preheat the oven to 350°F. Line a 1-pound loaf pan with parchment paper, letting it fold over the sides for easier removal.
To make the batter: In the bowl of a stand mixer fitted with the paddle attachment, add the butter, light brown sugar, and bananas, and mix on low until combined and there are no chunks of butter.
Add the buttermilk and eggs and mix on low until combined.
Add flour, cinnamon, baking powder, cinnamon, and sea salt into the mixing bowl in that order. Mix on low until combined, and you have a smooth batter. Fold in the blueberries.
Pour the batter into the loaf pan and spread out evenly. Bake for 1 hour and 15 minutes or until a wooden pick inserted in center comes out clean. Once the loaf has cooled, remove it from the pan.
Store in an airtight container for up to 7 days.
Video
Notes
High Altitude — Bake at 350°F for 1 hour or until a toothpick inserted in the center comes out clean.