Rub the butter into the flour until the
mix looks like fine breadcrumbs. Stir in
the icing sugar, then make a well and use
a round-bladed knife to stir in the oil, egg
yolk and 1½-2 tbsp cold water until dough
comes together. Without overhandling,
gather into a ball. On a lightly floured
surface, roll out so it fits a 23 x 2cm
loose-bottom flan tin. Ease the pastry
into the tin, then trim the edges by rolling
the rolling pin over the top. Press the
pastry into the flutes so it sits very
slightly proud of the edge (this extra
height helps in case of any shrinkage).
Lightly prick the pastry base with a fork,
then chill for about 10 mins. Heat the
oven to 190C/170C fan/gas 5.
Meanwhile, make the filling. Beat the
eggs and egg whites together with a
wooden spoon until well mixed. Sift the
icing sugar into a bowl, then gradually
beat in the eggs. If the mix is at all lumpy,
simply beat with a wire whisk. Stir in the
lemon zest and the juice. Leave to stand
so the lemon flavour can develop.
Sit the chilled pastry case on a baking
sheet. Line with baking parchment and
baking beans and bake blind for 20 mins
until well set. Carefully lift out the beans
and paper, then bake the pastry case for
another 3-5 mins until the base is cooked
and pale golden.
Strain the lemon mixture through a
sieve. Beat the crème fraîche in a
medium bowl until smooth, then slowly
stir in the lemon mix until well blended.
Transfer to a jug, then carefully pour two
thirds into the warm pastry case. Place
in the oven with the oven shelf half out,
pour in the rest of the filling, then
carefully slide the shelf back in. Reduce
the heat to 150C/130C fan/gas 2. Bake
for 25-30 mins until barely set with a
slight wobble in the middle. Cool for
about 1 hr, then serve with a light dusting
of icing sugar. Best eaten the same day.