Preheat the oven to 400f/200c and line a baking tray with baking parchment. Place the flour, salt and butter into a large bowl and rub together with your fingertips until the mix resembles breadcrumbs. Add the sugar, cranberries and orange zest and give it a mix.
Break the egg into a small bowl, give it a quick whisk with a fork and then pour it into the flour mixture – reserving 1 tbsp of it for glazing the scones later.
Add in the ¾ of the buttermilk and the vanilla extract and use a round ended knife to work the mixture together. Add the rest of the buttermilk and work in gently until you have a soft, slightly sticky dough. Don't overwork, or you'll get tough scones.
Tip out the dough onto a floured surface and flatten it out with your hands into a round shape, about 1” (2.5cm) thick. Use a sharp knife and cut the circle into 8 wedges.
Place the wedges onto the prepared baking tray. Mix the reserved tbsp of egg with the splash of milk and brush the tops only (brushing the sides will impair the rising of the scones) with this mix and place in the oven for 12-15 minutes until golden brown.
Remove from the oven, leave to cool and serve sliced in half with clotted cream and jam/jelly.