In a medium bowl, combine the sliced strawberries, 1/4 cup granulated sugar, and lemon juice. Stir gently, then set aside to macerate for at least 30 minutes. The sugar will draw out the juices, creating a sweet syrup.

Preheat oven to 400°F (200°C). Line a baking sheet with parchment paper. In a large bowl, whisk together the flour, 1/4 cup sugar, baking powder, and salt. Using a pastry cutter or your fingers, cut in the cold butter until the mixture resembles coarse crumbs with some pea-sized pieces.

In a small bowl, whisk together 2/3 cup cold heavy cream, the egg, and vanilla. Pour into the flour mixture and stir with a fork until a shaggy dough forms. Turn out onto a lightly floured surface and gently knead 3-4 times until it comes together. Pat into an 8-inch circle, about 3/4-inch thick. Cut into 8 wedges. Place wedges on the prepared baking sheet, brush tops with a little heavy cream, and sprinkle with a pinch of sugar. Bake for 20-25 minutes, until golden brown. Let cool completely on a wire rack.

While the shortcake cools, make the whipped cream. In a chilled bowl, using a hand mixer or stand mixer with the whisk attachment, beat the 1 1/2 cups heavy cream, 1/4 cup powdered sugar, and vanilla on medium-high speed until stiff peaks form.

Once the shortcake wedges are completely cool, carefully split each one in half horizontally using a serrated knife. Place one shortcake bottom on a serving plate. Spoon a generous amount of the macerated strawberries and their syrup over it. Top with a large dollop of whipped cream. Place the matching shortcake top gently over the cream. Repeat with remaining wedges to make 8 individual servings.

Top each assembled cake with an extra spoonful of whipped cream and a few reserved strawberry slices or a whole strawberry. Dust lightly with powdered sugar and serve immediately.