Preheat oven to 350F and line a baking sheet with parchment paper.
In a large bowl, sift together all dry ingredients. Whisk well to combine.
In a measuring cup, combine egg and buttermilk, set aside.
Cut cold butter into peanut sized chunks. Try not to handle butter too much so it stays cold.
Toss butter into your dry ingredients with your hands to coat.
Squeeze flour and butter with your hands to create large flakes. There will still be a lot of dry flour, but all butter should be flakes and not chunky.
Pour this mixture onto the counter and make a well in the center.
Add half of the buttermilk mixture (pour it around the lip) and toss with your hands.
Add remaining buttermilk and toss until mostly combined. There will be a lot of dry flour still.**
Using a plastic bowl scraper, gather and fold the dough onto itself and press down. Do this about 4 times or so until the dough mostly comes together. There will still be some flour showing.
Form into an 8" disc and place on parchment baking sheet. Chill for 20mins.
Trim the edges of the disc to allow the scones to rise, cut into 8 wedges.
Bake in a circle with the edges close together so that the edges stay soft.
Egg wash only the top of each scone (do not let it drip down the sides).
Sprinkle with coarse sugar if desired.
Bake for 15-20mins until golden.
Notes
*You can try substituting 400g (3cups) all purpose flour if you don't have bread and pastry flours. ** If adding berries or chocolate chips add now.