Preheat the oven to 400°F (200°C) and line a baking sheet with parchment paper. Set aside.

In a medium bowl, combine the flour, sugar, baking powder, and salt, then cut in the butter with a pastry blender until the mixture is crumbly.

In a separate medium bowl, whisk together the sour cream, eggs, and vanilla extract, then stir into the dry ingredients just until a dough is formed.

On a lightly floured surface, pat the dough into a 5x10-inch (12½x25½-cm) rectangle that is 1 inch (2½ cm) high.

Cut the shortcake lengthwise down the middle, then cut each half into 4 squares. Transfer to the prepared baking sheet, spacing them evenly apart.

Brush the tops of the shortcakes with the milk and bake for 18 to 20 minutes or until golden and firm when tapped lightly. Let cool completely, for about 1 hour.

In a large bowl, combine the berries with the desired amount of sugar and let them macerate at room temperature.

In the bowl of a stand mixer fitted with a whisk attachment or with a medium bowl and a handheld electric mixer, whip the cream to soft peaks. Refrigerate until needed.

When ready to serve, split the shortcakes in half horizontally and place the bottoms on individual plates. Divide the berry mixture among the shortcakes, then top with a big dollop of whipped cream and place the shortcake tops on the cream. Serve immediately.