Preheat oven to 400⁰F (205⁰C).
In a large bowl, whisk together flour, sugar, baking powder, baking soda, cinnamon & salt.
In a separate bowl, whisk together melted butter, egg and buttermilk.
Add to dry ingredients and stir, until just combined. Fold in chopped apple.
Spoon batter into muffin tin and bake 20-22 minutes, until golden brown and tops spring back when lightly touched. Transfer to wire racks to cool.