Preheat the oven to 350ºF and adjust the rack to the middle position. Put unbleached muffin liners into a muffin pan, or butter each muffin cup in a 12-cup pan. 

Place the butter in a small saucepan over low heat. Melt and continue to cook until the milk solids are golden to dark brown. Cool for 5 minutes. 

Place the bananas, eggs, cane sugar and vanilla in a large bowl and stir to combine. Stir in the cooled brown butter.

In a medium bowl, combine the almond flour, arrowroot, baking soda, cinnamon, and sea salt, Stir to combine.

Add the dry ingredients to the banana mixture and stir until combined. 

For the cinnamon topping: Place the sugar, butter, flour and cinnamon in the food processor and process until combined. 

Spoon the batter into each muffin cup, filing up about 3/4 of the way up. Put a small amount of the cinnamon topping on top of each muffin, distributing evenly. Bake for 23 minutes, or until edges are just golden brown.