Preheat oven to 400ºF
In a large mixing bowl, combine flour, baking powder, baking soda, and salt.
Cut in butter until mixture is crumbly.
Separate the egg white and yolk. Set the egg white aside.
In a smaller bowl, mix egg yolk, honey, and buttermilk (or milk/lemon juice mixture).
Add wet ingredients to the dry ingredients and stir until just combined.
On a floured work surface, form the dough into a ball.
Roll or pat the ball into a half-inch-thick disc, roughly 8 inches in diameter.
Cut dough into eight equally-sized pieces.
Transfer the dough to a greased baking sheet (a pie spatula makes this very easy).
Whisk the egg white until froth forms and brush over the tops of the scones.
Mix turbinado and cinnamon together and sprinkle over egg-white-topped scones.
Bake in preheated oven for 10 to 12 minutes.
While scones bake, mix powdered sugar, milk, and vanilla until a thin glaze forms.
Drizzle glaze over scones after they come out of the oven.