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 forms a ball. Add additional water only if necessary.
02 - Form dough into a disc, wrap tightly in plastic wrap, and refrigerate for at least 30 minutes. On a lightly floured surface, roll out dough and press into a 9-inch tart pan. Trim edges and prick bottom with fork. Chill for 15 minutes.
03 - Preheat oven to 375°F. Line crust with parchment paper and fill with pie weights or dried beans. Bake for 15 minutes. Remove weights and parchment, then bake 8–10 minutes longer until golden brown. Cool completely before filling.
04 - Heat whole milk in a saucepan until just simmering. Meanwhile, whisk egg yolks, sugar, and cornstarch in a bowl until mixture turns pale and thick, about 2 minutes.
05 - Slowly pour hot milk into egg mixture while whisking continuously. Return mixture to saucepan and cook over medium heat, whisking constantly, until thickened and bubbles form, about 2–3 minutes. Remove from heat.
06 - Stir butter and vanilla extract into hot cream until smooth. 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 strawberries, raspberries, blueberries, and kiwi slices decoratively over cream.
08 - Warm apricot jam with water in a small saucepan until melted. Strain through fine mesh sieve and brush evenly over fruit. Refrigerate assembled tart for at least 30 minutes before serving.