Sift plain flour and icing sugar into a bowl and rub in butter cubes until the mixture looks like breadcrumbs.
Add the beaten egg yolk and work into a dough, adding ice-cold water if the pastry is too dry.
Wrap the pastry in cling film and chill in the refrigerator for at least 10 minutes.
Preheat the oven to 180°C.
Roll out the pastry on a floured surface to 5mm thickness.
Cut pastry circles and line 10cm tart cases, pressing the edges firmly.
Prick bases with a fork and line with aluminium foil and ceramic baking beans.
Bake for 15 minutes until crisp, then remove beans and foil to cool on a wire rack.
Heat milk in a large pan until it just reaches boiling point.
Whisk egg yolks, flour, and caster sugar, then slowly whisk in the hot milk.
Return the mixture to the pan and stir constantly over medium heat until thickened.
Transfer crème pâtissière to a bowl and dust with icing sugar to cool.
Sieve the apricot jam and heat with 30ml of water to create a smooth glaze.
Fill tart cases with crème pâtissière, top with fruit, and brush with the apricot glaze.