Combine dry ingredients in a food processor. Pulse/stir to mix. Add butter and mix until crumbly. Mix sour cream egg yolk, and orange juice. Stir into dry ingredients (will be dry). Kneed to combine. Divide in half. Shape into 6" rounds. Place on a greased baking sheet lined with parchment paper. Cut into 6 wedges. Beat egg white until frothy, brush over tops, and then sprinkle with sugar crystals. Bake at 375 degrees for 25 to 30 minutes.