Preheat oven to 375°F and line a sheet pan with parchment paper.
In a large bowl, combine the all purpose flour, sugar, salt, and baking powder. Add the citrus zest. Add the cubed butter and cut into the dry ingredients with a pastry cutter or fork until the butter is the size of peas.
In another bowl, whisk together the buttermilk, egg, and 1 tablespoon of citrus juice. Add to the dry ingredients and stir with a spoon just until the mixture comes together and all the dry bits are incorporated.
Pat out on a lightly floured surface to about 1 ½ inches thick. Cut out rounds and place on the prepared sheet pan about 2 inches apart. Brush the tops with eggwash. Bake until golden, about 12 to 15 minutes.
Meanwhile, combine the powdered sugar and remaining citrus juice to make a glaze. Cool the baked scones on a wire rack and spoon glaze over the tops while they're still warm.
Notes
Note: Feel free to use oranges, tangerine, clementines, manadarin oranges, and even lemons or limes.Adapted from Martha Stewart