1. Preheat oven to 350°F (175°C) and line a six-cup muffin tin with paper liners or grease lightly.

2. In a bowl whisk together all-purpose flour, baking powder, ground cinnamon and salt until evenly combined.

3. In a separate bowl whisk melted butter with brown sugar and granulated sugar, then beat in egg, milk or buttermilk and vanilla extract.

4. Pour wet ingredients into the dry mixture and gently fold until just combined, leaving the batter slightly lumpy.

5. Fold the peeled and diced apple into the batter until evenly distributed.

6. Spoon the batter into the prepared muffin cups, filling each about three quarters full.

7. Bake for 18 to 22 minutes until the tops are golden and a toothpick inserted into the center comes out clean.

8. Allow muffins to cool in the tin for five minutes, then transfer to a cooling rack to cool completely.

9. Store cooled muffins in an airtight container at room temperature for up to two days or freeze individually for longer storage.