Place the oven rack in the top third position and preheat to 350°F. Line a sheet pan with parchment paper.
In a small bowl, whisk together the egg, yolk, and 1 cup of heavy cream until evenly mixed. Set aside.
In a large bowl, whisk together the flour, 1/3 cup sugar, kosher salt, and baking powder.
Add the cold, grated butter and use your hands to coat the butter in flour until you have walnut-size pieces.
With a spatula or wooden spoon, fold in the egg and cream mixture until a sticky (but not wet) dough forms. It should almost look like sugar cookie dough—soft yellow color and able to hold together when pressed.
Use a greased (with nonstick spray) 1/3 cup measure to scoop out the dough onto the lined sheet pan. Place them evenly across the pan with about 2 inches between each shortcake. Place the pan in the freezer for 10 minutes.
Meanwhile, in a medium bowl, stir together the sliced strawberries, sugar, salt, and vanilla until the strawberries are evenly coated. Cover and place in the refrigerator.
Remove the shortcakes from the freezer and brush the remaining 2 tablespoons of heavy cream on top of each one, then sprinkle the remaining tablespoon of sugar on top.
Place the shortcakes in the oven and bake until the tops are a light golden brown and the centers are baked through, about 24-26 minutes.
Remove from the oven and let cool until no longer warm to the touch, about 15 minutes.
While the shortcakes are cooling, add the heavy cream, sour cream, sugar, and vanilla to a large bowl and use a hand mixer to whip to soft peaks. Do not overwhip. Remove the strawberries from the refrigerator and stir again. The strawberries should have softened slightly and there should be a clear-ish syrup at the bottom of the bowl.
Once the shortcakes are fully cooled, split in half horizontally. Place a large dollop of whipped cream on the bottom half of each cake, then spoon sliced strawberries and a bit of the syrup on top of the whipped cream. Finally, place a small dollop of whipped cream on top of the strawberries and cap with the top half of the shortcake. Serve and enjoy immediately!