- 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.