Preheat oven to 160°C/140°C fan/gas mark 3/320°F.
Whisk the flours together in a large mixing bowl then add the butter, rubbing together with your fingertips to create breadcrumbs.
Add the sugar, baking powder and salt and mix well.
Pour the milk into a jug and whisk in the eggs until just combined then pour into the centre of the scone mixture.
At first stir the liquid ingredients in with a wooden spoon then tip out onto a clean work surface and using your hands bring the dough together, turning and folding, until it is no longer sticky. Use a bit of extra gluten-free flour on the work surface if it is starting to stick.
Once you have brought the dough together into a ball, press it down into an even circle 1 inch thick.
Cut out the scones using 7cm cutter.
Place the scones onto a clean baking tray. Whisk the extra egg yolk with a couple of teaspoons of buttermilk (or regular milk) and brush onto the surface of each scone, making sure not to let it drip down the sides, else your scones will not rise evenly.
Bake the scones for 18 minutes. Let the scones rest on the baking tray for 5 minutes then remove and let cool on a wire rack.