Preheat waffle iron to desired heat level.
Combine the flour, baking powder, baking soda and salt in a large mixing bowl.
In a medium bowl or 4-6 cup measuring cup, whisk together the buttermilk, eggs, vanilla, maple syrup and melted butter until well blended. (A blender can do this easily, too.)
Pour the wet mixture into the dry ingredients and stir until just combined.
Brush the inside of the waffle iron with coconut oil and spoon about a scant ½ cup of batter onto the middle. Add blueberries, chocolate chips or diced banana to the surface, if desired. Close the waffle iron and follow the manufacturer’s directions for cooking the waffles.