Sift the flour, baking powder, baking soda and salt together in a large bowl. Set aside.
Slice the orange into quarters and remove the seeds, as well as the peel if using Valencia oranges (see notes). Place in a blender along with the fresh orange juice and blitz into a fine puree.
Now preheat the oven to 180 C and line 12 muffins moulds with liners or grease them.
In a mixing bowl, beat the butter and sugar until pale and fluffy, then add the egg. Beat to combine.
Add 1/4 of the flour mixture (to stabilise the batter), then add the pureed orange. Fold slowly to combine and though the acid in the orange will likely cause the mixture to split, it will be ok at the end!
Add the remaining flour mixture gradually, then run the hand mixer through it to make a smooth batter.
Divide equally among the muffin moulds and bake for 20 to 25 minutes until browned on top and a toothpick poked in the center of the muffins comes out clean. For even browning, rotate the tray halfway through baking.
Allow the muffins to cool in the moulds for 10 minutes, then place on a wire rack to cool completely. Store in an airtight tin for 2 to 3 days at room temperature, then transfer to the fridge for a week or the freezer for about a month. Happy baking!