For the Shortcakes:

1. Preheat your oven to 375°F (190°C).
2. In a large bowl, whisk together the flour, sugar, baking powder, and salt.
3. Cut the cold cubed butter into the dry ingredients using a pastry cutter or your fingers until the mixture resembles coarse crumbs.
4. In a small bowl, whisk together the heavy cream and egg. Pour the wet ingredients into the dry mixture and stir gently with a spoon until just combined.
5. Turn the dough out onto a lightly floured surface and gently knead it a few times to bring it together. Pat the dough into a 1-inch thick rectangle.
6. Use a round biscuit cutter (or a drinking glass) to cut out shortcakes from the dough. You should get about 6-8 shortcakes.
7. Place the shortcakes onto a baking sheet lined with parchment paper. Brush the tops with a little heavy cream.
8. Bake for 15-18 minutes, or until the shortcakes are golden brown. Allow them to cool slightly.

For the Filling:

1. In a medium bowl, combine the sliced strawberries, granulated sugar, and lemon juice. Stir to coat the strawberries and set them aside for about 10 minutes, allowing the strawberries to release their juices.

For the Whipped Cream:

1. In a large mixing bowl, whip the chilled heavy cream, powdered sugar, and vanilla extract together using an electric mixer until soft peaks form. Be careful not to overwhip.

Assembling the Shortcakes:

1. Slice each shortcake in half horizontally.
2. Spoon some of the sweetened strawberries and their juices onto the bottom half of each shortcake.
3. Add a generous dollop of whipped cream on top of the strawberries.
4. Place the top half of the shortcake on top and garnish with a few more strawberries, whipped cream, and fresh mint leaves, if desired.