Preheat oven to 350 degrees and spray a 9x9 inch square pan with non-stick spray and line with parchment paper.

In a large bowl, whisk together the flour, xanthan gum, baking powder, baking soda, salt, and granulated sugar.

In a separate bowl, whisk together the mashed banana, brown sugar, oil, eggs, milk, and vanilla extract. Pour the wet ingredients into the dry ingredients and stir to combine.

Pour the batter into the prepared pan and bake at 350 degrees for 25-30 minutes or until a toothpick or cake tester comes out clean or with a few moist crumbs attached. Cooking time will vary depending on your oven - mine took 29 minutes.

Cool the bread in the pan on a cooling rack. Cut into 16 pieces and serve slightly warm or room temperature.

To store, wrap tightly in foil or store slices in an air-tight container. It will stay fresh up to 3 days. This bread also freezes well. To freeze, slice into individual pieces and freeze in a freezer bag.