01 - Preheat the oven to 350°F. Line a baking sheet with parchment paper.
02 - In a bowl, combine flour, powdered sugar, and salt. Cut in cold butter until mixture resembles coarse crumbs. Add egg yolk and 2 tablespoons cold water; mix until dough comes together, adding more water if needed. Shape into a rectangle, wrap in plastic, and chill for 20 minutes.
03 - Roll dough to 1/4-inch thick rectangle, approximately 9x12 inches. Trim edges for clean appearance. Transfer to prepared baking sheet. Prick surface with fork. Bake for 20-25 minutes until golden brown. Cool completely.
04 - Heat milk with vanilla bean in saucepan until just simmering. Whisk egg yolks, sugar, and cornstarch until smooth. Gradually whisk hot milk into egg mixture. Return to saucepan and cook over medium heat, whisking constantly, until thickened for 3-4 minutes. Remove from heat, discard vanilla bean, and stir in butter. Cool completely.
05 - Spread cooled vanilla cream evenly over cooled pastry base.
06 - Arrange fruits on top of cream in envelope or love letter shape. Use strawberries for envelope flap and remaining fruits for decorative filling.
07 - Heat apricot jam with water until melted. Strain mixture, then brush gently over fruit for glossy appearance.
08 - Refrigerate tart for at least 30 minutes before slicing and serving.