01 - Preheat oven to 350°F. Grease a 9-inch tart pan with a removable bottom.
02 - In a large bowl, combine flour, granulated sugar, salt, and chilled butter. Using fingertips, rub butter into flour until mixture resembles coarse crumbs. Add egg yolk and 2 tablespoons cold water. Mix just until dough forms, adding extra water if needed.
03 - Press dough evenly across the base and sides of the tart pan. Refrigerate for 20 minutes.
04 - Line crust with parchment paper and place baking beans or pie weights inside. Bake for 15 minutes. Remove weights and bake an additional 5 minutes or until golden. Set aside to cool completely.
05 - In a bowl, whisk mascarpone, powdered sugar, vanilla, and lemon zest until smooth. In a separate bowl, whip heavy cream to soft peaks. Gently fold whipped cream into the mascarpone mixture.
06 - Spread mascarpone filling evenly over the cooled tart shell.
07 - Decoratively arrange strawberries, blueberries, kiwi, raspberries, and preferred seasonal fruits over the filling.
08 - Warm apricot jam with 1 tablespoon water until smooth. Gently brush glaze over fruit to provide a glossy finish, if desired.
09 - Refrigerate assembled tart for at least 30 minutes to set before slicing and serving.