Mix the cornflour with the egg yolks then whisk into the milk until smooth. Put back on the heat and cook over medium whisking continuously until a thick custard is formed. Remove from heat and stir every few minutes to prevent a skin forming.
Preheat the oven to 180 degrees C.
Quickly rub the flour, salt and butter together. Form into a rough ball and roll thin between greaseproof paper so that it fits a 23cm flan tin. Lay it into the tin to line the bottom and up the sides. Put it into the freezer for a few minutes.
Cover pastry with buttered aluminium foil and bake in preheated oven for 20 minutes. After the 20 minutes are up, look under the aluminium foil to see if the pastry is cooked through; bake a little longer if necessary. Remove the flan tin from the oven then immediately and carefully remove the aluminium foil.
In the meantime, scrape vanilla beans from the pod, add them to the milk and sugar and bring to the boil.
Spread the raspberry jam over the cooled pastry case and fill with the still warm custard and smooth out. Place raspberries on top and gently push them into the custard slightly. Allow the tart to set for 2 hours in the fridge before eating.