In a large bowl, combine flours, arrowroot, baking powder, xanthum gum, salt, cinnamon and sugar. Mix together thoroughly.
In a second small bowl, whisk the egg until it is sudsy. Add oil, vanilla and milk. Whisk together. Pour wet ingredients into dry. Add mashed banana, melted nutbutter and ⅓ C chocolate chips. Fold together with a spatula until all is just combined, 15 to 20 strokes. Let sit for 5 minutes before filling muffin cups.
Line a 6 cup pan with paper cups. Evenly distribute the batter between 6 cups, it will fill all the way to the top. Sprinkle the top of the muffins with more chocolate chips and turbinado sugar.
Place in preheated oven. After 2 minutes, reduce the heat to 375 degrees. Bake for 25-27 minutes until tops spring back when gently pressed.
Remove from oven. Serve warm. Store leftovers in an airtight container and refrigerate.