Preheat the oven to gas mark 6 or 200 degrees celsius.
In a large bowl, add the flour, xanthan gum and baking powder and mix well. Add the butter and rub between your fingers to form breadcrumbs.
Add the caster sugar and mix well.
To form a dough, add the egg and milk and stir. (Add the sultanas at this point if you are using them).
On a floured surface, roll (or pat) out the dough until it's approximately 3 cm thick.
Use a 6 cm cutter and place the scones onto a baking tray (line with baking parchment if not non-stick)
Brush with beaten egg and bake for 15 minutes or until golden.
Serve with clotted cream and jam (in either order - your preference!) and enjoy!