Begin by preheating your oven to 350°F (175°C). This ensures that your banana bread bakes evenly and rises beautifully.
In a large mixing bowl, whisk together the large egg, Greek yogurt, and liquid-state coconut oil until smooth. Add the light and dark brown sugar, vanilla extract, cinnamon, and nutmeg. Whisk until the mixture is creamy and well combined.
Add the mashed ripe bananas to the wet mixture. Use a fork or a potato masher to blend the bananas into the batter, making sure to keep some small chunks for added texture.
In another bowl, mix the all-purpose flour, baking powder, baking soda, and a pinch of salt. Stir to combine.
Gradually add the dry ingredients to the wet mixture, stirring gently until just combined. Be careful not to overmix; a few lumps are perfectly fine!
Gently fold in the frozen blueberries, ensuring they are evenly distributed throughout the batter.
Grease your loaf pan with a little coconut oil or cooking spray. This will help your banana bread slide right out once it’s baked.
Pour the batter into the prepared loaf pan and smooth the top with a spatula. Bake for 55-65 minutes or until a toothpick inserted into the center comes out clean.
Once baked, remove the banana bread from the oven and let it cool in the pan for about 10 minutes. Then transfer it to a wire rack to cool completely.
While your banana bread is cooling, whip up the blueberry butter. In a small bowl, combine the softened unsalted butter with about ½ cup of fresh or drained frozen blueberries. Use a fork to mash and mix until creamy and spreadable.
