01 - Pulse flour, sugar, and salt in a food processor. Add cold cubed butter and pulse until mixture resembles coarse crumbs. Add egg yolk and 1 tablespoon cold water, pulsing until dough just comes together. Add additional water only if necessary.
02 - Shape dough into a flat disc, wrap tightly in plastic wrap, and refrigerate for at least 30 minutes. On a floured surface, roll out dough and fit into a 9-inch tart pan. Trim excess dough from edges and prick base thoroughly with a fork.
03 - Chill lined tart pan for 15 minutes. Preheat oven to 375°F. Line crust with parchment paper and fill with pie weights or dried beans. Bake for 15 minutes, then remove weights and parchment. Continue baking 8–10 minutes until golden brown. Cool completely.
04 - Heat whole milk in a saucepan until just simmering. Meanwhile, whisk egg yolks, sugar, and cornstarch in a bowl until mixture is pale and thick, about 2 minutes.
05 - Slowly pour hot milk into egg mixture while whisking constantly. Return combined mixture to saucepan and cook over medium heat, whisking continuously, until thickened and bubbling for 2–3 minutes. Remove from heat immediately.
06 - Stir butter and vanilla extract into hot pastry cream until butter melts completely. Transfer to a clean bowl and press plastic wrap directly onto surface to prevent skin formation. Refrigerate until completely cold, at least 1 hour.
07 - Spread chilled pastry cream evenly into cooled tart crust. Arrange fresh strawberries, raspberries, blueberries, and kiwi slices decoratively over cream surface.
08 - Warm apricot jam with 1 tablespoon water until melted. Strain through fine mesh sieve to remove solids. Brush warm glaze generously over fruit for glossy shine. Refrigerate completed tart for at least 30 minutes before serving.