How to Make It
Preheat the oven to 425°. In a food processor, pulse the flour, baking powder, granulated sugar and salt. Add the diced butter and pulse until the mixture resembles coarse meal. Add 3/4 cup of the cream and process until the dough just comes together.
Turn the dough out onto a lightly floured surface; knead 3 times. Roll out the dough 1/2 inch thick. Using a floured 2 3/4-inch round biscuit cutter, stamp out 8 shortcakes as close together as possible; transfer to a large baking sheet. Brush the tops of the shortcakes with cream and sprinkle with 2 heaping tablespoons of the turbinado sugar. Bake the shortcakes for 15 minutes, or until golden brown. Transfer to a wire rack to cool.
In a bowl, beat the remaining 2 cups of cream with 1/3 cup of confectioners' sugar and the vanilla until soft peaks form.
Melt the remaining 2 tablespoons of butter in a large skillet. In a bowl, toss the nectarines with the berries, the remaining 1/3 cup of turbinado sugar and the lemon juice. Add to the skillet and cook over high heat, stirring, until the fruit begins to release its juices, about 2 minutes. Remove from the heat.
Cut the shortcakes in half horizontally. Set the bottoms on plates; top with the fruit. Add a large dollop of whipped cream, close the shortcakes, dust with confectioners' sugar and serve.