Preheat oven to 350℉. Place 6 paper liners in a standard muffin tin.
In a medium bowl, whisk together dry ingredients. In a small bowl, whisk together the melted butter, sour cream, egg and vanilla. Add wet ingredients to dry ingredients and whisk well. Gently fold in the apples.
Spoon batter into liners.
Bake for 20-25 minutes until golden brown and the top is firm to the touch. Move muffins to a cooling rack and cool completely.
Notes
While regular cinnamon can be used in this recipe, Vietnamese cinnamon provides a stronger, richer flavor.