Preheat oven to 400°.
Combine milk and lemon juice in a medium bowl, whisk briefly, then let stand for 5 to 10 minutes.
Sift flours together. In a large bowl, combine sifted flours, brown sugar, baking powder, ground ginger, baking soda, salt and cinnamon, and whisk briskly. Stir in candied ginger and lemon zest until mixed throughout.
Cut butter into the flour mixture until it resembles mealy, coarse crumbs. Set aside.
Combine the molasses with the lemon juice-and-milk mixture. Add the egg yolk and whisk until smooth; stir into the flour mixture just until moistened. If dough is too crumbly to hold together, add a little more milk, 1 tablespoon at a time. Be careful not to over-mix.
Turn the dough onto a floured surface and knead gently 8 or 10 times. Pat the dough into a circle of roughly 8 inches and cut into 8 equal wedges. Transfer to a parchment-paper lined baking sheet, spaced at least 1 inch apart.
Beat the egg white with one tsp of water until frothy and brush over the scones. If using coarse sugar (recommended), sprinkle before baking.
Bake at 400° for 12-15 minutes or until golden brown. Transfer to a wire rack and cool for 5 minutes. Serve warm, dusted with powdered sugar if not baked with coarse sugar. Whipped cream is optional but it's sure tasty with these.