Preheat your oven to 450F.
Line a baking sheet with parchment. Place aside.
In a large bowl, mix the flour, 2 tablespoons of white sugar, 1 tablespoon lemon zest, salt, and baking powder.
Cut the cold butter into the flour mixture with a pastry cutter (you can do this in a food processor as well, but I prefer to do it by hand). Keep “cutting” the butter into the flour until the whole mixture looks like coarse crumbs.
In a small bowl, lightly beat the whole egg.
Add the milk, egg, and vanilla extract to the bowl with the dry ingredients. Stir together until everything is moistened. This is tricky – but you don’t want to over mix (that makes for tough shortcakes), but do your best. There will be some flour pockets left, which is okay.
Dump the dough out onto a well floured surface, and kneed for 8-10 pushes – just enough to bring it together. Shape & flatten the dough, using the palms of your hands, to a circle about 3/4 inch thick.
Using a lightly floured biscuit cutter, or 3-inch across drinking glass, cut out several circles, and transfer to a lined baking tray. You want to have 6-7 rounds. After the first cut, gently bring the dough together, and flatten again, to cut batch #2.
Once the shortcakes have been cut and transferred to the baking sheet, take a small bowl and fork-whisk together the egg yolk and the half & half for the glaze. Brush the tops of the shortcakes with this to glaze.
Sprinkle the tops with turbinado sugar (sugar-in-the-raw).
Bake for 12-15 minutes, or until perfectly golden.
Transfer to a wire rack to cool.