01 - Preheat oven to 350°F. Lightly grease a 9-inch tart pan with removable bottom.
02 - In a large mixing bowl, combine flour, granulated sugar, salt, and chilled butter. Rub butter into the dry ingredients until the mixture forms coarse crumbs. Add the egg yolk and 2 tablespoons cold water; mix just until it forms a dough, adding the extra tablespoon of water if needed.
03 - Firmly press dough into the bottom and sides of the tart pan in an even layer. Refrigerate the pan for 20 minutes to allow the dough to firm.
04 - Place parchment paper over the chilled dough and fill with baking beans or pie weights. Bake for 15 minutes, remove weights and paper, then bake 5 minutes more until golden brown. Allow crust to cool completely in the pan.
05 - In a bowl, whisk mascarpone cheese, powdered sugar, vanilla extract, and lemon zest until smooth. In a separate bowl, beat heavy cream to soft peaks. Fold whipped cream gently into the mascarpone mixture until incorporated.
06 - Spread mascarpone filling evenly into the cooled tart shell, smoothing the top with a spatula.
07 - Arrange strawberries, blueberries, kiwi, raspberries, and other seasonal fruits decoratively over the filling.
08 - Warm apricot jam with water until fluid. Gently brush the glaze over fruit to add sheen, if desired.
09 - Refrigerate tart for at least 30 minutes to set filling prior to slicing and serving.