Preheat: preheat an oven to 424.4°F (218°C) and adjust the rack to use the middle and low positions. Line 12-Muffins pan with muffin liners.
Mixing bowls: Prepare two mixing bowls; one for dry and another for wet ingredients.
First bowl: In the first bowl, sift the flour, xanthan gum, baking powder, bi-carbonate soda, salt, cinnamon, and nutmeg together and set aside.
Second bowl: In the second bowl, add and mix all wet ingredients, which are melted butter, brown sugar, egg, vanilla extract, and milk, and whisk well until light and fluffy, then add the mashed bananas and mix again until all combined.
Combine wet and dry: Pour the wet ingredients mixture into the dry ingredients bowl.Add the dark, white chocolate chips and almond flakes (reserve around 3 TBSP for topping later), then use a spatula to stir all ingredients until 'just' combined, around 8-10 folds. (See recipe note #1) Filling the tray: Fill around 2/3 of each muffin liner with the batter (around two scoops each). Sprinkle some reserved almond flakes on top of each muffin for extra crunch.
Baking: Bake the muffins for 20-24 minutes or until golden.Ensure to check the muffins after 15 minutes, as aluminum foil may be needed to cover the muffins to prevent the almond flakes from over-browning. Cooling: Leave the muffins in the pan for 5 minutes to cool down slightly before removing them onto the cooling rack. Allow the muffins to cool completely before serving. Enjoy them all on the same day, or keep them in an air-tight container for up to 7 days.