Preheat the oven to 375°F. Grease a 12-cup muffin pan, or line the pan with papers, and grease the papers., Whisk together the baking powder, baking soda, xanthan gum, salt, cinnamon, and flour or flour blend. Set aside., Beat together the soft butter, sugar, and molasses., Beat in the eggs one at a time, scraping the bottom and sides of the bowl between additions., Add the dry ingredients to the mixture in the bowl in three parts, alternately with the mashed bananas, beating well between additions and scraping the bottom and sides of the bowl one or two times during this process., After everything is added, scrape the bowl again and beat at medium high speed for 30 seconds, Stir in the walnuts., Scoop the batter into the prepared pan, mounding the cups full. The batter will rise above the level of each cup; that's fine., Bake the muffins for 22 to 25 minutes, until the middle springs back when lightly touched. Remove from the oven and let rest for 5 minutes before removing from the pan. Best served warm.