Pre-heat the oven to 325 F, 160 C, Gas 3.
Prep a 12-hole muffin tray with muffin cases.
Mix the demerara sugar and cinnamon together in a small bowl.
In a large bowl, mix the gluten-free flour, Bicarb of soda, and gluten-free baking powder.
Fold in the golden caster sugar and cranberries.
In a jug, beat an egg, add the sunflower oil and milk, and combine.
Zest the orange into the flour mixture.
Add the freshly squeezed orange juice to the jug and mix thoroughly.
Pour the wet ingredients into the dry and fold them gently together.
Divide the mixture evenly between the 12 muffin cases.
Sprinkle the top of the batter with the sugar and cinnamon mixture.
Bake in the oven for 20-25 minutes.Allow to cool on a wire rack before devouring.