Make the tart dough: Whisk flour, sugar, and salt. Cut in cold butter until mixture resembles coarse crumbs. Mix in egg yolk and 1 tablespoon ice water until dough forms, adding more water if needed. Shape into a disk, wrap, and refrigerate for at least 1 hour.
Roll and blind bake the shell: Roll chilled dough into a 12-inch circle. Press into the tart pan, trim excess, prick the bottom with a fork, and freeze for 15 minutes. Preheat oven to 375°F (190°C).
Line the shell with parchment and fill with pie weights. Bake for 15 minutes. Remove weights and parchment, brush with beaten egg, and bake another 5-7 minutes until golden brown. Cool completely in the pan.
Make the pastry cream: Heat milk with half the sugar until steaming. Whisk egg yolks with remaining sugar until pale, then whisk in cornstarch. Temper the eggs with hot milk, then return to the pan and cook until thickened. Remove from heat, whisk in butter, vanilla, and salt. Strain, cover with plastic wrap, and chill for at least 1 hour.
Assemble the tart: Spread chilled pastry cream evenly into the cooled baked shell. Arrange sliced peaches and strawberries over the cream in overlapping rows or a circular pattern.
Glaze and finish: Warm apricot preserves with water in a small saucepan until melted and smooth. Strain through a fine-mesh sieve and brush the glaze evenly over the fruit. Garnish with fresh mint leaves if desired. Slice into 8 pieces to serve.