Heat oven to 200C/180C fan/gas 6.
Roll out 250g of the pastry on a sheet
of baking parchment to about 25cm
square. Scatter over half the almonds,
then press them in very gently, dust
with half the icing sugar and lay over
a second sheet of baking parchment.
Lift onto a baking sheet, and sit another
baking sheet on top like a sandwich.
Fill a few small tins with baking beans
(or something similarily heavy and
ovenproof like raw rice). Bake for
30 mins, then have a quick peek – it
will probably need another 5 mins
to be well browned and crisp all over.
When done, remove from the oven,
take off the weights and top baking tray,
then carefully lift off the top sheet of
parchment and leave to cool. Repeat
with the remaining pastry – you can do
both sheets at once if you have enough
baking sheets and tins, but they might
not cook as evenly with two in the
oven, so it is safer to do one at a time.
Cool both completely.
Put the gelatine in a bowl of cold
water to soften, then put the remaining
custard ingredients in a big saucepan.
Set over a low heat to start, whisking
continuously to mix well, then increase
the heat a little until the custard is gently
boiling. Keep whisking the whole time
– the custard will thicken and lump
unevenly, but keep cooking and whisking
until it is smooth and very thick.
Remove the custard from the heat and
remove the vanilla pod. Squeeze out the
water from the gelatine sheet, then stir it
into the custard until it has dissolved.
Line the base and sides of a 20cm
square tin with baking parchment –
criss-crossing 2 big strips will give you
the neatest corners. Using a big, sharp
knife and a ruler – or the base of your tin
if it is removable – trim one pastry sheet
to a shade under a 20cm square, so it
will sit inside the tin, almond-side down.
Spread over the custard as evenly as you
can. Trim the second pastry sheet in the
same way, but then divide the square
into eight 10 x 5cm rectangles (so it will
be easier when you cut the slices later).
Sit them on top of the custard, almondside
up, putting them back together a bit
like a jigsaw puzzle. Gently press down
on the pastry so it doesn’t break but
sticks to the custard, then cover and chill
for 4 hrs or so, but better still overnight.
To serve, lift the slice from the tin and
cut all the way through where the pastry
top is already cut. Dust the slices with
a little more icing sugar and serve.
Best eaten within 24 hours, when the
pastry is still good and crisp.