Preheat the oven to 375°F (190°C) and line a baking sheet with parchment paper. Set aside.
In a large bowl combine the flour, sugar, baking powder, baking soda, salt and orange zest.
Rub the butter into the flour mixture using a pastry blender or your fingers until it resembles coarse breadcrumbs.
Whisk the egg and buttermilk together in a small bowl, then stir into the flour mixture.
Mix the dough very lightly until it just comes together, then transfer to the prepared baking sheet and shape into 7 inch (18 cm) disk, about 1-inch (3 cm) high.
Cut into 8 wedges, giving about 1 inch of space between each scone. Brush the tops only with egg wash.
Bake for 25-30 minutes or until golden brown. Transfer to a wire rack to let cool before serving.
