1. Line a muffin tin with muffin liners and preheat the oven to 350ºF.
2. In a large bowl or mixer, combine the mashed bananas, eggs, coconut oil, vanilla extract and nut butter until fully combined.
3. Add the coconut flour, cinnamon, baking soda, baking powder, and sea salt to the wet ingredients and mix well. Fold in the blueberries.
4. Pour the batter into the prepared pan and spread it evenly.
5. Bake in the preheated oven for about 11-13 minutes for mini muffins or 22-25 minutes for regular sized muffins, or until a toothpick inserted into the center comes out clean.
6. Remove from oven and allow in the pan for 10 minutes, and then remove from pan and let cool completely on a cooling rack.