To make pastry: Using fingertips, rub butter into flour until mixture resembles coarse meal; stir in sugar and egg yolks; press mixture together to form a ball and refrigerate in plastic wrap for 30 minutes; preheat oven to 375°F.
Roll pastry between two sheets of wax paper, making the pastry large enough to cover base and sides of a buttered 9-inch fluted tart pan; trim edges; place sheet of foil into pastry and fill with pie weights or dried beans; bake 20-25 minutes; remove foil and beans and bake a further 5 minutes; allow to cool.
To make custard: In medium bowl, whisk egg yolks, sugar and flour until thick and pale; heat milk in saucepan until almost boiling; remove from heat. Slowly dribble in hot milk into egg mixture, whisking continuously, until all of milk has been added. Return custard to pot and cook, over medium-low heat, until custard has thickened and coats the back of a spoon (5-7 minutes). Place piece of plastic wrap directly onto surface of custard (this prevents a 'skin' from forming) and allow to cool completely.
To assemble: Spoon custard into baked pie shell and smooth. Place pieces of fruit attractively over tart. Heat apicot jam until it is quite liquid and brush this generously over the fresh fruit to set and seal the tart. Allow to cool completely.
Serve the same day of making. Refrigerate any leftovers.