Preheat the oven to 350°F, and line a 9x5 bread pan with parchment paper.
Melt the butter in a saucepan on the stove. In a large bowl, mash the bananas until smooth.
Pour the melted butter into the bowl, and mix with bananas until well combined.
Add baking soda, salt, cinnamon, and sugar, and mix thoroughly.
In a separate mixing bowl, whisk the eggs together with the vanilla until smooth, and then add them into the batter. Gradually stir in the coconut flour and mix until well combined.
Pour the batter into the prepared bread pan, spreading it evenly.
Bake for 45-55 minutes, or until the top is golden brown and a toothpick comes out clean.
Remove from the oven, and let it cool before slicing. Enjoy!