Cut the rhubarb into 10.5cm batons,
using pieces that are roughly the same
width. Put the vanilla pod, sugar, lemon
juice and 300ml water (or enough to just
cover the rhubarb) in a wide frying pan or
shallow casserole set over a low heat.
Once the sugar has dissolved, add the
rhubarb and simmer for 5 mins. Remove
from the heat and leave to cool in the
syrup, preferably overnight, or for at least
1 hr. This way your rhubarb should be
perfectly cooked, but still hold its shape.
To make the pastry, put the flour,
almonds, sugar and butter in a food
processor. Blitz until the mixture
resembles breadcrumbs. While the motor
is running, add the egg yolk and dribble
in 1-2 tbsp cold water. Tip onto a work
surface and knead briefly to bring the
mixture together to form a dough. Wrap
in cling film and chill for 30 mins.
While your pastry chills, make the crème
patisserie. Heat the milk and reserved
vanilla seeds in a pan set over a medium
heat until nearly boiling. Meanwhile, whisk
the egg yolks, sugar and flours together in
a large bowl until pale. Continue whisking
while you pour the hot milk over the egg
mixture. Wipe out the saucepan and strain
the liquid back into the pan through a
sieve. Set over a medium-low heat and
stir continuously until the mixture has a
thick custard consistency. Scrape into a
clean bowl, cover the surface with cling
film to prevent a skin from forming and
chill for at least 1 hr or up to 2 days.
Remove the pastry from the fridge.
If it is a little hard, leave it at room
temperature to soften for 10 mins or so.
Roll out to 1mm thick on a lightly floured
surface. Use the pastry to line a 12 x 35cm
fluted rectangular tart tin, making sure
you press the pastry into the fluted edges
(you can use the blunt end of a knife
to help you do this). Leave any excess
pastry overhanging. Chill for 30 mins.
Heat oven to 200C/180C fan/gas 6.
Remove the pastry case from the fridge,
line with baking parchment and fill with
baking beans. Blind-bake for 20 mins, then
remove the parchment and beans, and
continue baking for 8 mins more until pale
golden and biscuity. Use a sharp serrated
knife to trim off the overhanging pastry
to give you a clean edge. Cool in the tin.
Remove the rhubarb pieces from their
syrup and set aside. Return the syrup to
the hob and boil until thick and sticky.
Leave to cool slightly. To finish the crème
patisserie, whisk the cream until it holds
soft peaks and fold this into the chilled
mixture. This is easier if you start by
beating in a little cream and then folding
in the remaining.
Remove the pastry case from the tin
and put on a plate. Fill with the crème
patisserie and smooth over the surface.
Carefully line up the rhubarb down the
length of the tart case, trying to fit them
in quite snugly. Use a pastry brush to
glaze the tart with the rhubarb syrup.
Chill for 30 mins before serving. This tart
will keep for 3 days in the fridge, however
it is best eaten on the day it is made.