Make the shortcakes:
Preheat the oven to 425ºF with a rack in the middle. Lightly butter a baking sheet.
In a small bowl, stir together the sliced strawberries with the sugar. Set aside.
In a large bowl, whisk together the flour, baking powder and salt. Stir in the heavy cream just until a dough forms. Gather the dough into a ball and knead it on a lightly floured surface one to two times. (Don't over-knead the dough or your biscuits will be tough.)
Roll out the dough until it's 1/2-inch thick. Using the cookie cutter, cut out 8 shortcakes and transfer them to the baking sheet.
(Alternately, you can trim the sides of the dough into a square and then, using a sharp knife, cut the dough into 8 square shortcakes.)
Brush the tops of the shortcakes with additional heavy cream and then sprinkle them with the sanding sugar (optional). Bake the shortcakes until golden, 15 to 20 minutes, and then transfer them to a rack to cool.
Make the whipped cream:
In the bowl of a stand mixer fitted with the whisk attachment, whisk the heavy cream, sour cream, sugar and vanilla extract on high speed until soft peaks form.
Assemble the shortcakes:
Slice the shortcakes in half and then sandwich the strawberries and whipped cream inside them.