01 - Preheat oven to 350°F. Grease a 9-inch tart pan with removable bottom.
02 - In a large bowl, combine flour, granulated sugar, salt, and butter. Rub the butter into the flour mixture until it resembles coarse crumbs.
03 - Add egg yolk and 2 tablespoons cold water to the mixture. Mix until a dough forms, adding an extra tablespoon of water if needed.
04 - Press dough evenly into the tart pan. Refrigerate for 20 minutes to firm up.
05 - Line the crust with parchment paper and fill with baking beans or pie weights. Bake for 15 minutes. Remove weights and parchment, then bake for 5 minutes more until golden. Cool completely.
06 - In a bowl, whisk mascarpone, powdered sugar, vanilla extract, and lemon zest (if using) until smooth. In a separate bowl, whip heavy cream to soft peaks, then gently fold whipped cream into mascarpone mixture.
07 - Spread mascarpone filling evenly in cooled tart shell.
08 - Arrange strawberries, blueberries, kiwi slices, raspberries, and any other preferred fruit decoratively over the filling.
09 - For a glossy finish, warm apricot jam with water until liquid. Brush over fruit using a pastry brush.
10 - Refrigerate tart for at least 30 minutes to set before slicing and serving.