For the pastry, place the flour, sugar, salt, vanilla seeds and butter in a food processor. Use the pulse setting to mix until combined. Add the beaten egg and milk, then pulse again until the dough comes together and leaves the sides of the bowl.
Turn out the dough onto a very lightly floured work surface. Shape into a ball and wrap in cling film and place in the fridge for at least an hour before using. (The pastry can also be made ahead and frozen or kept in the fridge for up to four days.)
Preheat the oven to 180C/320F/Gas 4.
Once chilled, on a floured work surface roll the pastry out thinly. Line a 20-23cm/8-9in flan or quiche dish with the pastry. Place some baking parchment in the middle and fill with baking beans. Bake for 30 minutes or until the pastry is a light golden-brown (to blind bake – the pastry should not be completely cooked).
For the crème pâtissière, in a pan bring the milk and vanilla pod to the boil. Remove from the heat and set aside to infuse.
In a bowl, cream together the egg yolks and sugar until pale and fluffy, then add the flour. Remove the vanilla pod from the hot milk and set aside. Pour the milk over the egg yolk mix and stir well. Return the mixture to the pan and warm, stirring continuously, over a medium heat until it is thick enough to coat the back of a spoon.
Remove from the heat. Place a fine sieve over a bowl and strain the crème pâtissière into it. Cover with clingfilm so that the clingfilm sits directly on the crème pâtissière (to prevent a skin forming) and refrigerate until completely cooled.
Fill the pastry case with the crème pâtissière and smooth the surface with a pallet knife or the back of a spoon.
For the fruit topping, arrange the strawberries, raspberries, blackberries and redcurrants over the top. Chill in the fridge until needed.
For the jelly, warm half of the champagne in a pan over a low heat. Add the sugar and cook until melted, then add the softened gelatine and stir well. Pour in the rest of the champagne and stir. Transfer to the fridge to cool. When the jelly is nearly set spoon it over the fruit tart and smooth the surface.
Chill in the fridge until the jelly has set completely.