Combine the flour, sugar, and salt in a mixing bowl. Cut in the cold, diced butter using a pastry cutter or your fingertips until the mixture resembles coarse crumbs. Add the egg and mix until the dough comes together. Wrap in plastic and chill for 15 minutes to relax.
Preheat your oven to 350°F (175°C). Roll out the chilled dough on a lightly floured surface to about 1/8 inch thickness. Cut out circles to fit your tart pans or muffin tin cups. Carefully fit the dough circles into each cavity, pressing gently to remove air pockets.
Prick the bottom of each tart shell with a fork to prevent bubbling. Bake in the preheated oven for 15 minutes, or until golden around the edges. Remove from oven and let cool on a cooling rack.
In a bowl, whisk together the mascarpone cheese, powdered sugar, and vanilla extract until smooth and creamy. Set aside.
In a small saucepan, combine sugar, lemon juice, and cornstarch. Cook over medium heat, whisking constantly, until the mixture thickens and begins to boil. Remove from heat and pour into a bowl to cool slightly.
Once the lemon curd has cooled enough to handle, spoon or pipe a layer into each cooled tart shell. Spread it evenly to cover the base.
Top the lemon layer with the mascarpone mixture, gently spreading it over the curd to create a smooth, creamy layer.
Arrange the halved or sliced strawberries on top of each tartlet, pressing gently into the mascarpone to secure. Use a variety of colors for a vibrant look.
Chill the assembled tartlets in the refrigerator for at least 30 minutes to set everything together and enhance flavors.
Serve the tartlets chilled, garnished with additional strawberries or a sprinkle of powdered sugar if desired. Enjoy the crisp crust contrasted with creamy layers and fresh fruit.
