Prepare the Strawberries: In a medium bowl, combine sliced strawberries, sugar, and lemon juice. Gently stir and let macerate for at least 30 minutes, stirring occasionally.
Make the Shortcake Dough: Preheat oven to 400F (200C). In a large bowl, whisk together flour, sugar, baking powder, and salt.
Cut in the Butter: Cut in the cold butter using a pastry blender or your fingertips until the mixture resembles coarse crumbs.
Add Wet Ingredients: In a small bowl, combine heavy cream and beaten egg. Add to the dry ingredients and stir until just combined. Do not overmix.
Shape and Bake: Turn the dough out onto a lightly floured surface and gently pat it into a 1-inch thick circle. Use a 2 1/2-inch biscuit cutter to cut out rounds. Place the rounds on a baking sheet lined with parchment paper.
Bake: Bake for 18-20 minutes, or until golden brown. Let cool on a wire rack.
Make the Mascarpone Cream: In a medium bowl, combine cold mascarpone cheese, cold heavy cream, powdered sugar, and vanilla extract. Beat with an electric mixer until stiff peaks form. Be careful not to overbeat.
Assemble the Shortcakes: Split each shortcake in half horizontally. Spoon a generous amount of mascarpone cream onto the bottom half of each shortcake. Top with the macerated strawberries. Place the top half of the shortcake over the strawberries.
Serve: Serve immediately.
Optional Tips:
- For a tangier flavor, substitute buttermilk for the heavy cream in the shortcake dough.
- A sprinkle of lemon zest can brighten the mascarpone cream.
- If mascarpone isn't available, use a high-quality stabilized whipped cream or crme frache for a similar, though slightly less rich, result.