Thoroughly mix the baking powder, sugar, salt, rice flour, potato starch, tapioca flour, arrowroot flour and xanthan gum together.
Mix in the eggs, milk, melted butter and vinegar. Stir until they just begin to blend. Finally, add the blueberries and stir in just until mixed.
Pour batter into a greased/paper lined muffin tin. Sprinkle a bit of sugar on top, then bake at 400F for 20 to 25 minutes, or until internal temperature of muffin reaches 205°F, using an instant read thermometer.