In a food processor, pulse the oats for 20 seconds, until they look like whole wheat flour, but not totally pulverized. It should make almost ½ c of coarse oat flour. ( You can skip this step if using whole wheat flour or all-purpose flour; *see note).
In a medium mixing bowl, whisk together grinned oats, flour, sugar, baking powder, soda and salt.
Grate chilled butter right over the dry ingredients. Cut in with pastry cutter or use your fingers to combine everything to coarse crumbs.
Add raisins to butter flour mixture and stir with a wooden spoon.
In a small mixing bowl, whisk together egg and buttermilk. Add to dry ingredients and stir just until all is combined.
Dust counter top or large silicone pastry mat with flour. Place dough onto the surface. Pat into a 1 inch thick disk. Fold the dough like letter. Pat down into 1 inch thick disk again. With a floured 2 and ½ inch biscuit cutter, cut out scones. Place on prepared sheet. Gently gather the remaining dough into a disk without kneading it. Cut out more biscuits. Use this way all the dough.
In a small mixing bowl, whisk together egg yolk and orange juice (or half and half, cream or milk). Brush the tops of the scones with the egg wash. Sprinkle about 1 teaspoon of oats on top of each brushed scone.
Bake for 12 to 15 minutes, or until the tops are golden and start to brown around the edges.
Cool on sheet for 2 minutes, transfer onto cooling rack to cool completely.