Combine Dry Ingredients: In a large bowl, whisk together the flour, sugar, and salt.
Cut in the Butter: Add the cold, cubed butter to the flour mixture. Using a pastry blender or your fingertips (work quickly), cut the butter into the flour until the mixture resembles coarse crumbs.
Add Ice Water: Gradually add the ice water, one tablespoon at a time, mixing gently after each addition. Stop adding water when the dough just comes together and is slightly moist but not sticky.
Form the Dough: Gently gather the dough into a ball. Flatten it into a disc, wrap it tightly in plastic wrap, and refrigerate for at least 30 minutes, or up to 2 hours.
Roll Out the Dough: On a lightly floured surface, roll out the dough into a 12-inch circle (about 1/8 inch thick).
Transfer to Tart Pan: Carefully transfer the rolled-out dough to a 9-inch tart pan with a removable bottom. Gently press the dough into the bottom and up the sides of the pan.
Trim and Crimp the Edges: Trim any excess dough from the edges of the pan. Crimp the edges of the crust using a fork or your fingers to create a decorative border.
Pre-Bake the Crust: Preheat your oven to 375°F (190°C). Line the crust with parchment paper and fill it with pie weights or dried beans. Bake for 15-20 minutes, or until the edges are lightly golden brown.
Remove Weights and Bake Further: Remove the parchment paper and pie weights. Return the crust to the oven and bake for another 5-10 minutes, or until the bottom of the crust is golden brown.
Cool Completely: Let the crust cool completely in the tart pan before adding the filling.
Soften Mascarpone Cheese: Make sure your mascarpone cheese is softened to room temperature.
Whip Heavy Cream: In a large bowl, whip the heavy cream until stiff peaks form.
Combine Mascarpone and Sugar: In a separate bowl, beat the softened mascarpone cheese with the granulated sugar until smooth and creamy.
Add Lemon Juice, Zest, Vanilla, and Salt: Add the fresh lemon juice, lemon zest, vanilla extract, and salt to the mascarpone mixture. Mix until well combined.
Fold in Whipped Cream: Gently fold the whipped cream into the mascarpone mixture until just combined.
Pour Filling into Crust: Pour the lemon mascarpone filling into the cooled tart crust. Spread the filling evenly to create a smooth surface.
Chill the Tart: Cover the tart with plastic wrap and refrigerate for at least 2 hours, or preferably overnight.
Garnish (Optional): Before serving, garnish the tart with fresh berries, a dusting of powdered sugar, and lemon slices, if desired.
Slice and Serve: Carefully remove the tart from the tart pan by lifting it from the bottom. Slice the tart into wedges and serve immediately.
Notes
Use cold ingredients for the crust.
Don’t overwork the dough.
Pre-bake the crust to prevent a soggy bottom.
Use fresh lemon juice and zest for the best flavor.
Chilling the tart is essential for the filling to set.