Preheat the oven to 425°F 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.